


Fundamentals for the Aspiring Assassin

by spontaneite



Category: Assassination Classroom
Genre: Fix-It, Gen, Time Travel
Language: English
Status: In-Progress
Published: 2017-03-13
Updated: 2018-06-23
Packaged: 2018-10-03 19:25:35
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 35,993
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10255859
Author URL: https://archiveofourown.org/users/spontaneite/pseuds/spontaneite
Summary: Nagisa was the first to notice when reality split apart, most likely because it happened directly beside him.





	1. Chapter 1

Nagisa was the first to notice when reality split apart, most likely because it happened directly beside him.

It was just a glimpse. Something appearing in his periphery that hadn’t been there a moment ago. Distracted, he turned his head towards it, knife lowering from the ready stance, and saw it. Just a glimpse, where it looked like light was bending and fracturing, like the air itself was paper, like something was pushing through-

A thunderclap resounded directly beside him, shockingly loud, and hot winds from nowhere blasted him off of his feet along with most of his assassination volleyball team. Nagisa heard alarmed screams and yells erupting around him, and he just barely made use of his lessons to take the fall properly, wincing at the impact of his leg and arm on the ground. Still, it wasn’t a bad fall, and he was among the first springing back to their feet after the unexpected blow. A small storm of dust had been whipped up by whatever-it-was, particularly where it had originated. Nagisa squinted in the direction he’d been thrown from, and could just about make out the sight of something…metallic?

“What the hell was that?” Maehara screeched, on behalf of probably everyone. Nagisa looked towards his voice, waving the dust from in front of his face. The redhead was on the other side of the net, which incidentally had been blown over. It looked like he’d been caught under the net, and had perhaps narrowly avoided a pole to the face. Terasaka had been caught by the net as well, but it seemed like everyone else on that side had been clear. On his side, though…

“Is everyone okay?” Karasuma-sensei demanded, rushing over from the sidelines. “What happened? …Did someone detonate a bomb?” It was a marker of their weird classroom that this seemed a perfectly sensible question to ask in such a circumstance.

Unexpected sort-of explosions weren’t so unusual, here. And, well…Despite the grenade incident being quite far in the past, everyone still looked at Nagisa. He wilted slightly under the stares. “Ah…Not me?”

From the floor, Okajima squinted at him. “You were closest to where it went off.” He was only now picking himself up, which was either an indication that he needed more falling practice or that he had a terrible reaction time. Maybe both.

“I saw something just before,” Nagisa mumbled, and looked back to the thing he’d seen. The dust was still swirling, catching unpleasantly in his throat as he breathed, but it had calmed enough to view the shape of the mystery object. “And there’s something there.” He resorted to pointing, because apparently looking at him and Karasuma-sensei was so interesting that no one else had thought to look towards the source of the impromptu wind-blast yet.

Obligingly, twenty-seven sets of eyes looked to the side. It would have been twenty-eight, but Karma was skipping – he always seemed to miss the interesting things. The dust obligingly settled into a restless stirring by the ground as they stared, revealing what certainly seemed to be an extremely large suitcase. Or maybe a safe with handles? It was a large, heavy-looking thing, with a hard shell and expensive-looking lock that covered a fair portion of one of its sides. A thing which had, apparently, appeared from nothing.

“…It’s a suitcase.” Sugino observed, baffled, as the other half of the team pulled the net off of their fellows and rushed over to investigate. “ A _suitcase._ That wasn’t there a minute ago, right?” he looked around, almost pleadingly. “Right?”

“It wasn’t.” Isogai agreed, staring at it. For a moment, no one spoke or moved, more than slightly flummoxed by the spectacle. Then, shrugging, Maehara stepped forwards and strode up to the suitcase.

“Stop.” Karasuma-sensei’s voice cut sharply across the field, even though he didn’t speak especially loudly. Maehara froze in place along with all the rest of them – their teacher had a pretty commanding presence to him, after all. He pushed through the crowd, waving Maehara out of the way, and cautiously regarded the case from three metres away. “A suitcase just appeared from _thin air._ That is not normal.” He pointed out dryly. “It would be irresponsible for me to allow any of you to come into contact with it. It could be dangerous.”

Nagisa blinked, rubbing a residual ache out of his arm as he watched.

“Back up. All of you.” The man added, crossing his arms. He stared out impassively at them until, reluctantly, the closer students backed away. His stare remained until they were all a good ten metres away – excessive, by some standards, but Nagisa could see the logic. If it were a bomb of some sort, for example, ten metres might not be nearly far enough.

Karasuma-sensei sighed at them, then turned warily to the case. He stared at it for several seconds in silence. Nagisa wondered what he was looking for. Triggers? Signs of a countdown? All he could see from this distance was the lock on the side, which seemed to have some sort of intricate mechanism on it, even a small screen. It looked more like something you’d expect to find on a high-security door than a suitcase.

For that matter…the suitcase looked _very_ well-armoured. Nagisa would flat-out call it a large safe if not for the obvious wheels and handles. He shared a bemused glance with Kayano, wondering what Karasuma-sensei would do with it. Would he approach it himself, or was he too wary? Would he call his bosses before approaching, or investigate himself?

“Nagisa-kun.” Karasuma-sensei said, out of nowhere. Nagisa looked up, startled. “What do you know about this?”

And, suddenly, everyone was looking at him again. “…Sensei?” He ventured, taken aback.

“The case has your name on it.” Their assassination instructor informed him, plainly. He pointed to the locking mechanism, presumably at a set of characters too distant to make out.

… _What?_ Nagisa stiffened, his first inclination to deny it, but...Karasuma wasn’t really the sort to joke about anything. “I-it does?” Why on earth would a suitcase appearing from thin air have _his name_ on it? The idea was _absurd._ His next breaths came too quickly for his liking, and he clamped down on the panic with rigid control.

“’Shiota Nagisa’.” Karasuma-sensei read out, slow and measured. “You can come and stand beside me to read it, if you don’t believe me.”

Feeling the weight of his class’ eyes on him, Nagisa swallowed, forcing his muscles to loosen. After a careful breath, he walked out from beside his classmates and approached his teacher, peering forwards. From this distance…the characters stood out in relief, plain and dark on the metallic lock. His eyes widened.

“Is it really your name, Nagisa-kun?” Nakamura called across the meagre distance. He glanced back, and found everyone stewing in varying flavours of curiosity and impatience.

“Ah…it is.” He confirmed, probably a bit too quietly for the furthest people to hear him. He nodded, hesitantly, if only to confirm it to himself. His name was on a spontaneously appearing suitcase. What on earth was someone meant to do in such a situation?

“I will ask again, Nagisa-kun. Do you know anything about this?”

Nagisa looked back at Karasuma-sensei. He was, admittedly, quite fond of the man. He was a good teacher, professional, and had respect for his students. It was nice to have the honest regard of an adult like him. He had no desire to disappoint the man. The only thing he could really do was be honest, even if the truth was difficult to believe. “I don’t know anything, sensei. I think it appeared next to me, but…” he trailed off, shaking his head. “Sorry.”

Karasuma regarded him calmly for several moments, then nodded. “Alright. Well then, what to do about this…”

Nagisa relaxed, very slightly, at the indication that he’d been believed. “Karasuma-sensei, do you think we should get Korosensei to look at it? If it’s dangerous, he’s least likely to be hurt.” And, naturally, if it was dangerous and he _was_ hurt, all the better.

“Quite true.” Karasuma nodded, pensive. “Logically, however, this is related to that octopus or assassination of him – something so unusual happening here is unlikely to be unrelated. If it _is_ related to assassination, it could be a bad idea to let the target see it. It could be a weapon, and secret weapons are best kept hidden.”

“Ah…” Nagisa dipped his head, frowning lightly. “Who would send us a weapon by teleportation without leaving something more to go on?”

“Who would send _you_ a weapon, Nagisa-kun.” The man pointed out. “It has your name on it.”

“Is there anything else written on it?” They both turned at the sound of Maehara’s voice, calling across the distance mandated by their instructor. Both of them absorbed the question and turned to investigate.

Nagisa scrutinised the case. It was at least a metre long, laying on its front with a liberal coating of dust and dried grass. It was also thick enough that the lock was basically a large metal plate on its armoured side, where the large characters of his name were written. But on the screen, which was darker, something could conceivably be written in small letters. “Can I go closer to see, sensei?” he asked, after a moment.

Karasuma scrutinised the case and sighed. “It hasn’t exploded yet, so I will go closer. You stay here and be ready to run.” He said, and walked forwards to close the meagre distance, kneeling down to read. He paused. “Hm.”

“Sensei?” Nagisa inquired, noticing that his classmates were inching closer in what they probably thought was stealthy. He made a face at them, receiving several rude faces in return. Maehara even stuck out his tongue.

“It says ‘present thumbprint’.” Karasuma said, and after a second did precisely that, demonstrating none of the caution and restraint they might have expected from him.

“Karasuma-sensei!” Nagisa, plus at least four of his classmates, protested – far too late to be of any use.

“Hm!” Karasuma expressed, this time sounding quite surprised. He looked at Nagisa, and then frowned, eyes fixing on the troupe of disobedient students that were certainly quite a bit closer now. “I said to stand clear!” he snapped.

“You’re letting Nagisa-kun near it, sensei.” Okajima pointed out, dropping the pretence of stealth and flat out striding over to the classmate in question.

_“Risking one student may be preferred to the whole class_.” Ritsu’s voice observed, at a slightly-too-low volume. Nagisa looked over and saw Kayano holding out the host phone. _“However, this item isn’t showing any signs of imminent combustion, and hasn’t moved since it arrived. It may prove dangerous, but most likely not until it is opened.”_

Kayano pressed her finger to the volume button on the side of her phone as she asked “Opened?”

_“The display is a fingerprint scanner.”_ Ritsu stated brightly. _“It must be connected to a locking mechanism.”_

“Did it reject your fingerprint, sensei?” Isogai inquired, coming to stand beside Nagisa.

“…It did.” Karasuma confirmed, and shifted out of the way to allow their view of the little screen. “Nagisa-kun, see for yourself.”

Nagisa leaned forwards and squinted to read it. “’Incorrect print. Two attempts remaining.’” He said aloud, narrowing his eyes. “...sensei?”

“It has your name on it.” The teacher stated, looking directly at him. “Will you try?”

He swallowed. “It might explode.”

“It might.” Karasuma acknowledged. “If yours doesn’t work, I’ll call my bosses and try to have it opened by professionals. It seems sensible to try your print first, however.”

Nagisa looked at his classmates, uneasy. As expected, all of them were staring at him. Some seemed a bit too eager, considering the potential danger of this. He looked back. “I’ll do it.” He said, settling slowly into the calm resolve that assassination called for.

With the same serious, respectful nod as he had that time, Karasuma stood up and stepped back. “Good. Everyone back up again – all the way to the school steps. If it does explode, there’s no sense in us all dying.” There was a fair bit of grumbling at that, but a sharp glance and a sharper word cut through it. “Now!”

“Harsh, sensei.” Terasaka grumbled, rolling a shoulder as he walked away with the others. “Oi, Nagisa, try not to blow up.”

Nagisa sighed, appreciating the irony of being told that by someone who’d once given him a grenade to suicide-bomb their teacher with. “Aa.”

Karasuma-sensei watched with a hawk-like eye until he deemed all of the students sufficiently distant. “Alright then.” He said, and Nagisa took it as the go-ahead it was. He shuffled forwards, kneeling down by the case to stare at his name, and the little screen. _‘Incorrect print. Two attempts remaining.’_ It read, unchanging. He exhaled, and reached out, pressing the thumb of his right hand firmly to the screen.

A moment passed. A light bleep sounded, and across the screen characters flashed – _‘Print accepted – Shiota Nagisa’_ – and then the front panel….hissed? There was a hissing sound, and a brief click. He removed his thumb, hesitant, and the panel immediately lifted away, springing up slightly on a mechanised hinge. He flinched back, wary of the potential of dire contents – but the case didn’t open. Only the front of the lock.

“Nagisa-kun?” Karasuma questioned, kneeling beside him.

“It took my print.” He murmured, carefully lifting the panel further up to see what was beneath. There was…another screen, a larger one, as well as a number pad. The screen bleeped, and text appeared on it. “…’Broadcasting’?”

“What does it mean by that?” Karasuma-sensei muttered, as if expecting Nagisa to know the answer.

“Sensei!” A voice called from a good distance, all the way over by the school. Kayano?

Karasuma didn’t look, eyes fixed on the display. “ _Stay there!”_ He ordered.

“Sensei!” Kayano called again, which was quite unusual for her. Nagisa looked over, and saw her brandishing her phone. “Something happened to Ritsu!”

At this first sign of trouble, Karasuma didn’t seem especially inclined to abandon the case. He had shown regard for Ritsu in the past, Nagisa had noticed, but certainly less than to the other students. That sentiment quickly shifted when all of their phones abruptly bleeped, buzzed, or otherwise indicated that they were restarting and installing upgrades.

“All of the phones…?” Kayano murmured, as Nagisa and Karasuma reached the crowd. “This can’t be a coincidence, can it?”

“Probably not.” Karasuma answered, checking a good five phones before he confirmed that they were all still loading. “The screen in the case said ‘broadcasting’ – most likely, it has broadcast something to your phones which has disrupted them.”

“What about Ritsu? Is she alright?” Nakamura demanded, staring at the screen of her phone with consternation.

“She had numerous hard copies. Even if her data is corrupted on every one of your phones, she should be fine.”

“Sensei?” Kayano presented the screen of her phone outwards, demonstrating the lit-up display. “Mine is starting up again.” Quite rapidly, the ranks of her classmates closed around her.

“Is it broken? Will it work?” Isogai asked the white light emanating from the screen, almost pleadingly. “I can’t afford another phone, it has to work!” He stared at his own device, which was still loading, a nervous tremor in the fingers gripping it.

“I think mine is finishing, too.” Okuda piped up, waving her smartphone.

“It’s finished booting.” Kayano said, quickly tapping in her passcode. Nagisa leaned over to watch as her phone desktop loaded, and a second later – “Ritsu is loading?” The screen had gone pink in the way that indicated Ritsu’s processes taking over the phone.

A moment later, as had become quite familiar, the pink-haired avatar of an artificial intelligence commandeered the screen, a lush and verdant background appearing behind her. There was a noteworthy difference, though. “Ritsu?” Nagisa asked, incredulous, and heard a ripple of shock pass over his class.

The avatar blinked the same unusual eyes that they were used to. The hair was the same style, and the same colour, but the face was indisputably older. Ritsu looked like a young adult, still fresh and bright, but certainly not someone you could mistake for a fifteen-year-old.

She smiled. _“Good morning, everyone!”_ She chirped from the phone speakers. A moment later, she loaded on Okuda’s phone, blinking from another screen, and took up her speech with two sets of speakers on the next sentence. _“It’s wonderful to see you all again!”_

“What happened, Ritsu?” Nagisa asked her as she activated on his own phone, and Sugino’s, and Kimura’s… “All of our phones suddenly crashed – was it something to do with that case?”

All of the Ritsu-phones paused, simulating a slow blink. It seemed most of the phones had booted her up by now. When she spoke, the voice came from over a dozen phones, and honestly the effect was more than slightly eerie. _“Yes, it was. The case broadcasted data intended for me._ ” She paused, which for her was a careful simulation of hesitance. “ _The data provided upgrades. I have updated myself on all of your phones, and that is why I look different.”_

“Ritsu.” Karasuma-sensei spoke clearly and calmly, his voice instantly cutting through the chatter as always. “Did the data include information about the case?”

_“It did.”_ Nagisa noted with amusement that Ritsu seemed to be present on twenty-six phones now, despite the fact that none of them were technically meant to have them during P.E class. The only person without one was their teacher himself.

When Ritsu did not elaborate, Karasuma frowned. “Please tell us everything you know.”

_“I am not permitted to tell you that._ ” Ritsu answered, far too cheerfully. A resounding silence fell at her flat-out, downright happy, refusal. Maehara whistled lowly, the sound carrying rather well in the hush.

“Why are you not permitted?” Karasuma demanded, stepping close to directly address Nagisa’s phone.

The avatar appeared to consider the question for a moment. Considering her processing speed, this was almost certainly another artifice. “ _The entirety of the information I have is only available to certain individuals under certain circumstances._ ” She oriented her eyes towards Karasuma-sensei, most likely using the front camera as a reference. _“There are some things I can tell you all. Firstly, I can induce this case to explode. Also, if anyone attempts to force it, it will detonate. The blast radius will be about forty metres.”_

Muttered curses swept around the clearing. The closest was Okajima, who uttered an impressed “Damn!” and inched backwards.

“Will anything else cause the case to explode?” Their special forces teacher asked, shoulders more intimidating than Nagisa was used to, and a rather severe expression settling onto his features. “Is there any other risk associated with it?”

_“I am installed in the case as a security precaution. If unauthorised individuals attempt to access the contents, or force their way in, I will make it explode.”_ Ritsu informed him, as though she were discussing ice cream flavours instead of what was essentially a bomb threat. _“There are items inside the case which can cause considerable harm if handled improperly, so improper handling is not advised.”_

“Why is my name on it? Why did it have my fingerprint?” Nagisa cut in, making all of the closest Ritsu-phones orient their eyes and faces in his direction. It was quite unsettling. Karasuma looked up at him, but didn’t say anything against the question. Clearly, he considered it pertinent.

Ritsu beamed at him. _“That’s because the case is for you, Nagisa-kun!”_

Nagisa stared. “Um…”

“Why Nagisa?” Karasuma cut in, swiftly.

Her voice was almost sing-song in cadence. _“I am not permitted to say.”_

Their instructor scowled. “Are you permitted to tell Nagisa, if the case is for him?”

Ritsu ruminated on the screen, averting her gaze demurely. A bird landed on her hair and chirped disarmingly. _“Nagisa-kun is allowed access to certain parts of the case, provided he follows instructions.”_ She said, hunching a little, as though feeling shy. _“But…I can’t tell you everything yet, sorry!”_

Karasuma sighed. “Right. And does this have anything to do with assassination?”

Ritsu’s young adult avatar widened her eyes, blinking endearingly. _“Ah…I can’t say.”_

“What I really mean by that is, should we avoid letting that octopus know about this case? Would it decrease our chances of a successful assassination?”

Bizarrely, the question seemed to alarm her. _“I can’t say. But...my opinion is that keeping Korosensei out of things is likely to be useful, at this stage.”_

“Right.” Karasuma-sensei nodded decisively. “Okay, everyone,” he pitched his voice to carry. “Since this might be related to assassination, no one is to mention it to your octopus of a teacher. If he asks about the damage to the field, you will say that an experimental assassination tool caused the damage, and that you sustained only very light injuries. You will refuse to give him more details if he asks, because giving too much information to your target is a bad idea. You should also attempt to keep him distracted during afternoon classes, where possible.” He turned to stare pensively at Nagisa. “Nagisa-kun, you’ll be working with me. It seems I will need your help to determine the facts about this case.”

“What if Korosensei asks where Nagisa-kun is?” Kayano asked, sensibly. “Nagisa-kun doesn’t usually skip class, so he probably won’t ignore it.”

“Hmm.” Karasuma frowned at Ritsu’s face on the screen. “You will tell him that I am giving Nagisa a special assassination tutorial related to the experimental tool, and that he isn’t allowed to interfere.” He was silent for several moments, and then continued. “No one is to ask Ritsu about this when he might be listening. Ritsu, can you simulate your previous appearance in class?”

The image on the screens, between one moment and the next, reverted quickly to the fifteen-year-old Ritsu avatar. _“Of course, sensei!”_

“Then it’s settled. I will be cancelling class to deal with this issue. You should exercise until the end of the period, don’t waste this time. Don’t practice with weapons without supervision.” Karasuma glanced sharply towards Nagisa, who had to admit to feeling exceptionally on-edge by this point. “Nagisa-kun.”

“Yes, sensei.” He nodded, and fell in line with the teacher as he strode back towards the case, Ritsu still occupying his phone screen. “Ritsu, is the case safe to move?”

_“Yes, but handle it gently. There are fragile things inside._ ” She paused, and added _“Isogai has sent you a message saying that the others want you to tell them anything you find out later.”_

“Don’t just say it out loud, Ritsu!” Nakamura shouted in the distance.

_“Ehehe. Sorry?”_

Karasuma emitted a very beleaguered sigh. Nagisa could sort of sympathise.

\---

“Is there anything else you can say now that it’s only us, Ritsu?” Karasuma asked, once he’d set the case carefully on the floor in his office. Nagisa hovered awkwardly in the corner, not especially comfortable in what was clearly a teacher-only space.

_“You do not have special permissions, Karasuma-sensei.”_ Ritsu chirped from the phone, still in Nagisa’s hand.

“What about me?” He inquired of the device.

_“You have special permissions, Nagisa-kun, but they will only be activated if you follow a particular set of instructions.”_

Karasuma motioned at him to be quiet, and demanded “Who issued the instructions?”

Ritsu smiled. _“Nagisa-kun did._ ”

There was a very protracted silence. “Eh?!” Nagisa spluttered, unable to keep the shock internal, because…what? “ _Me?”_

_“The contents of this case, and of the data upgrade I received, were assembled by you, Nagisa-kun.”_ The AI proclaimed, cheerfully indifferent to the emotional crises she was presenting him with. _“I am a security measure, and also a backup. If you decide not to carry out your instructions, I will detonate the case and carry out my own orders.”_

“W-what instructions?” Nagisa asked, unable to keep quiet. A glance to the side revealed an extremely sceptical glower on his instructor’s face. He didn’t believe her, then? Or, at least, he thought there was foul play involved.

_“My own instructions are classified. Yours will likely take a while to complete.”_

“What are the instructions for Nagisa-kun?” His teacher cut in, leaning a little closer to the phone than Nagisa was comfortable with. He quickly put the phone on the desk to make it more mutually accessible.

Ritsu’s expression brightened. “ _On the panel that opened on the side, you should see another screen. Please place and hold your finger on it, Nagisa-kun. Until it tells you to remove it.”_

Nagisa glanced at Karasuma, who held up a hand. Obediently, he remained still, and watched as his teacher interrogated what was technically another student. “Do these instructions pose any risk to Nagisa-kun?”

Ritsu was silent for at least three seconds, which was not reassuring. _“Completing the instructions will be physically unpleasant, and require an adjustment period. Full side effects are unknown. However, it is not expected that serious or permanent injury will result, provided the instructions are followed carefully.”_

He eyed her with alarm. “What if the instructions aren’t followed carefully?”

Ritsu made a face at him. _“Do you really need to know? If you’re careful, it’s not important.”_

“You can’t expect him to do something unless he knows the risks involved.” Karasuma pointed out. “Especially if he doesn’t know what he will gain from it.”

_“Hmph!”_ Phone-Ritsu crossed her arms, looking quite put-out. _“Nagisa-kun thought it was worth the risk, or he wouldn’t have given me the instructions!”_

“Just give an overview of the benefits and the risks, Ritsu. Please.” The man sighed, rubbing at his temples. Nagisa nodded fervently.

Ritsu stared out balefully from the screen. _“In the case, there are items which will allow Nagisa-kun to learn many new things very quickly.”_ She said. _“When the process is complete, he will have decades worth of information, including useful data on how to assassinate super-beings like Korosensei. He will also know everything about the case, including why and how he sent it.”_

Nagisa exchanged a wide-eyed glance with his teacher. “That…sounds very useful.” He said, a little reluctantly. “It also sounds like cheating, though.”

_“That’s silly, Nagisa-kun._ ”

“I agree. Information is an assassin’s greatest weapon.” Karasuma concurred quietly, the initial surprise settling into a considering frown. “And, if Ritsu is to be believed, you were the one to arrange all of this, despite how ridiculous it sounds.” His voice implied, very strongly, just how ridiculous he found it.

Nagisa was quiet for a moment while he thought. “Ritsu-chan,” he said. “Tell me the biggest risks, please.”

She pouted. _“Mou…well, the items necessarily act on your brain. If they are damaged, or interfered with improperly, they might do the wrong things and cause damage._ ”

His heart gave a sudden, distinct, heavy thump in his chest. Nagisa swallowed, thoughts of his mother’s violent mood swings searing through the front of his mind. “That sounds _horrible._ ”

_“We were careful, you know._ ” Ritsu said, plaintively. _“We don’t want you to get hurt, so we made it as safe as possible. Please just open the case? I’ll show you the items._ ”

Nagisa looked uneasily at his superior. Carefully, the man nodded, and Nagisa exhaled. “…Alright.” He approached the case and knelt down, flipping open the outer panel to expose the screen inside. He regarded it warily. Instead of ‘broadcasting’, it now read ‘present your thumb, Nagisa-kun!’. Moreover, the text was pink. Ritsu didn’t seem to be lying about her presence in the case, then.

With trepidation, he pressed his right thumb firmly to the screen and kept it there. In short order, the screen heated up, the characters ‘ _analysing!’_ flashing at the top.

_“The screen will feel hot until it finishes, Nagisa-kun. Please keep your thumb where it is.”_

Nagisa winced as the heat, slowly but surely, became painful on his skin. He took a deep breath, and remained still. By the time the screen cleared, he felt like he’d seared the finger on a stove, and it throbbed painfully.

_“Thank you, Nagisa-kun!”_ Ritsu chirped, and her words flashed on the screen in front of him. _“I can open the first portion of the case, now!”_

He backed away hastily as the central portion of the case’s lid unexpectedly lifted away. He wondered what the number pad was for, if it just needed some other sort of print to open. “It has separate sections?” Maybe the keypad was for the other sections?

_“Only this first section is available until you have completed your instructions.”_ Ritsu proclaimed. _“Have a look inside!”_

Karasuma knelt beside him as he pushed the lid back and looked.

The middle compartment was relatively small. The interior was extremely well-padded, with the shock absorption and thick walls taking up most of the space. Nagisa carefully lifted away a padding layer, and found a befuddling array of items.

There were two sturdy metal bottle of maybe half-litre capacity, and two syringes, complete with uncomfortably thick needles. There were also two metal cylinders. The largest item, though, was something that for all the world looked like a helmet. A thick metal helmet with _lots_ of wires, and also some sort of neck plating.

“What is he meant to do with this?” Karasuma asked, once enough time had passed with Nagisa unable to find his voice.

_“The bottles contain a fluid to be injected by the headset. The cylinders contain pills – one for pain, and the other to prevent bad reactions from your immune system.”_ Ritsu explained. _“This process will take anything from three days to two weeks. The first time you equip the headset, it will carry out a comprehensive scan of your brain and determine how long the process will take. You should do that now, Nagisa-kun – it won’t take long.”_

Nagisa stared at the headset that would apparently be manipulating his brain with no small amount of apprehension. “Will I be able to take it off?”

_“The headset is very advanced. For the scan, you will need to press a button and wait a few minutes to make it safe to remove. During the actual process, you can’t take it off at all.”_

He looked up. “…Sensei?”

Karasuma looked him directly in the eyes. There was no condescension there; not a hint of derision or cruelty. Only quiet, serious respect. “It’s your choice, Nagisa-kun. Information is very valuable, but we know too little about this situation to have any guarantees about the risks.”

Nagisa remembered another moment like this, another thought. _‘If he’s the one handing me the knife, I know I can trust him’, right? But…_ “Ritsu, if somehow it _was_ myself issuing these instructions, I would find it easier to trust in them.” He said, softly. “But it doesn’t make sense. How could I have done all of this and not remember it at all?”

Ritsu blinked at him from the smartphone screen. _“Eh? You didn’t figure it out?”_ She asked, surprised. _“Obviously it’s time-travel!”_

A pause.

_“What?!”_ Both of them shouted it; not quite at the same time, but almost.

Ritsu rolled her eyes and huffed. _“What did you think I meant, when I said you’d sent me? Some sort of complicated plot where you had your memory wiped?”_ Ritsu rolled her eyes at them, as though time travel were any less ridiculous than complex memory-wiping schemes. _“Sending objects back in time is quite easy, but we’ve found no way to make it work on living creatures._ _Thankfully, artificial intelligences like myself are easy to send back! Especially for me, since I already had a past self I could hack and overwrite!”_ She looked exceptionally pleased with herself at that.

“S-so, when you say _I_ arranged this and wrote the instructions, you mean it was _me in the future?_ ” Nagisa asked, feeling more shocked than he ever had in his life. He’d been quite sure that nothing would ever compare to the surprise of learning Class 3-E had become an assassination classroom. Clearly, he’d been very, very wrong.

_“Of course. I was an excellent candidate for time travel, but I am restricted to technology. You decided we needed to try restoring you, Nagisa-kun. That’s why this headset is primed with the details of your future brain._ ” Ritsu pointed towards the side of the screen closest to the case. “ _The technology has never been used to change an immature brain before, so we’re being very careful. There are other treatments in the case we can use to help you recover, if things don’t go well.”_

“So when you say _decades of knowledge_ , that’s decades of _future knowledge._ ” Karasuma exhaled slowly.

“Does that mean we killed Korosensei, if the memories are from more than a year in the future?” Nagisa asked, not certain he actually wanted to know the answer. On one hand, he swelled with anticipation at the possibility of such success, but on the other…he thought it might seem sort of hollow, finding out like this.

Ritsu frowned at him, an unusual expression for her face. _“I can’t tell you, Nagisa-kun. You’ll have to find out for yourself._ ”

Karasuma looked at him. “…I hate to say it, Nagisa-kun, but if this involves _decades_ of memory, it’s possible the problem is larger than your class’ assassination.” He pointed out. “Again, it’s completely your choice what to do.”

Nagisa stared into the case, thoughts and emotions at war. A large and sensible part of him was adamant that one should not risk permanent brain damage on the word of an artificial intelligence claiming borderline-unbelievable things. Unfortunately, the rest of him was quite stuck on the words _time travel,_ and was slightly too shocked to listen. He took a deep breath, and reached for the headset. “I can do the first scan, at least.”

_“Put it on, and press the button on the middle of the forehead.”_ Ritsu instructed, perking up at his apparent acquiescence.

The headset was heavy and cold in his hands. The interior was padded, and studded with odd ring-shaped pieces of metal. A large flap came down from the back of it, looking like it would envelop his neck, though he couldn’t see the fastenings. Carefully, he lifted the headset and put it on, feeling his hair ties prickle against his scalp. “Should I have my hair up?” He asked, a little uneasy.

Ritsu paused. _“Do the ties contain any metal?_ ”

“A little.”

_“It’s best you take them out, then.”_

Nagisa removed the headset, setting it gently in his lap, and reached up. His hair, as much as he detested its length, was relatively well-behaved; it took mere seconds of careful tugging to pull out the ties, allowing it to fall softly around his neck. He glanced to the side, finding a trace of curiosity in Karasuma’s eyes, and looked away. He put the headset on again, and reached up to his forehead to find the button. Pushing past his clamouring fears, he pressed it, and waited.

Abruptly, the neck-piece stiffened and closed around the sides of his neck, connecting at the front in a series of quiet clicks. Nagisa repressed the flash of panic at the feeling of pressure on his throat, and _waited._ He very determinedly did _not_ raise his hands to tear at the thing tightening on his neck, no matter how he disliked any sort of constriction near his airways.

The padding inside the headset seemed to expand, pressing against his scalp. It grew warm. The neck-piece tightened in several places, and loosened in a few others. Then, abruptly, he felt a stabbing pain at the back of his neck, like a thick needle. “You didn’t say anything about needles, Ritsu.” he muttered, clenching his fists. He shuffled to sit cross-legged on the floor beside the case, Karasuma kneeling seiza to watch him carefully, setting the Ritsu-phone beside him. The tightness of the neck-brace made it hard to move his head.

_“The headset is injecting a compound that will allow for more detailed scanning. This will take about fifteen minutes to complete._ ” She informed him.

“…Okay.” He made a face.

“Is everything alright, Nagisa-kun?” Karasuma requested, voice and face a little grim. He seemed tense. Was he worried?

“There was a sharp pain at the back of my neck. I can still feel it, but it’s not as bad now.” He answered, carefully keeping his hands still in spite of the urge to rip the helmet off. “…It’s only fifteen minutes.”

“This time.” His teacher reminded him, bleakly.

Nagisa frowned at his lap. “…Yeah.” He looked at the screen of his phone, his head far heavier than he was used to it being. “Ritsu-chan…you said the actual procedure will take days. Did…did _we_ plan for how to do that? It’s not like I could let my mother see this thing.”

“… _Oh._ ” Ritsu looked a little worried. _“The plan was just to have you go missing for the duration. I can access the headset’s scans and supervise you, to make sure you’re doing alright.”_ She hesitated, and added _“But...having someone to help would be very useful. You should really be unconscious for the active parts, and I don’t like the idea of you being vulnerable then.”_

Nagisa looked at his teacher expectantly, receiving a light grimace in turn. “I could supervise, but not for very long.” He said. “I can’t justify significant absences without informing my bosses, and somehow I doubt you will want that.”

_“Your bosses are very curious, Karasuma-sensei!”_ Ritsu said, bright and cheerful. _“If they try to interfere with the case, I will have to blow them up!”_ She sounded utterly unconcerned about the possibility.

Karasuma did not seem surprised in the least. “That is why I feel it would be a poor idea for me to be absent.”

_“Aa…you might just have to mysteriously go missing then, Nagisa-kun. I’ll do my best to take care of you._ ” Ritsu concluded, regretfully.

“I haven’t agreed to do it, yet.” He pointed out, closing his eyes. “Can you not tell me why this is important? It seems a lot of effort for me to go to when you know everything already. You could just tell me what I need to do.”

She blinked wordlessly for several seconds. He thought that such a span might be remarkable – what was she processing, for it to take her so long? _“A lot of our plans will need someone with a body who knows the things that you do, Nagisa-kun.”_ She said, finally. _“Knowing isn’t enough. You need to remember.”_

“And you can’t say _why?_ ” Nagisa asked, tiredly, opening his eyes again to look at his phone. He’d barely had a few days to get used to the idea that, maybe, he actually had some talent for assassination – and then something like this was dropped on him? “Or even why it was _me?_ ”

Ritsu, again, was quiet for an unusually long time. “ _We edited my code so that I would have to obey the last orders you gave.”_ She said. _“If you undergo the process successfully, I will be able to tell you anything. Until then…I only have a little leeway in my instructions. I can’t tell you why you did this, or when, or how.”_ A pause. _“But I can tell you that we did the bulk of our planning and research off-planet. I can also tell you that Earth would have had better facilities, with better resources.”_ She waited.

Karasuma eyed her from above. “…Don’t tell me – Earth was destroyed?”

_“I can’t tell you that.”_ Ritsu asserted.

“Can you tell me why you didn’t do the research on Earth?” Nagisa prodded, feeling the neck-cover tighten again. He twitched against the impulse to raise his hand to it.

She smiled. _“No.”_

“What planets were available as potential research bases?”

A pause. _“Mars was the only planet available.”_ She presented them with two thumbs-up, the sunlight brightening in her background. It was not especially congruent to his mood.

Nagisa swallowed, tension bearing down on him. “So, something bad happened to Earth, whether or not it was destroyed.” He concluded, heaviness settling into his veins. If that was the case, and his future self _had_ organised all of this, then…did he really have a choice? “I…suppose I have to, then. I have to try.” In a way, it was reassuring, knowing what he needed to do. On the other hand, anything with brain damage as a potential consequence _terrified_ him.

“Is this so much more frightening than being told to kill a super-being of a teacher?” Karasuma asked, glancing at his watch.

“Korosensei isn’t going to hurt me.” Nagisa said plainly. “This could.” He watched as the man’s head dipped in acknowledgement, and looked down at Ritsu again. “You must have prepared for the idea that I wouldn’t believe you about the time travel. Isn’t there anything else you can tell me? If you have information, do you have things like pictures, too?”

Ritsu bleeped. _“We didn’t think about the possibility of pictures.”_ She said, sounding surprised. _“I have many in my database, yes, and some might not count as off-limits information. What would you like to see?”_

“A picture of whatever happened to Earth.” He said, immediately.

Ritsu paused. _“I’m sorry, that isn’t allowed._ ”

Nagisa pondered it. “A picture of myself, then. As recent to the time travel as possible.”

_“Retrieving data._ ” A moment later, her image was replaced with a picture of him taken from the front, cropped so that only his head and shoulders were visible. Nagisa leaned in, fascinated.

He looked noticeably older. His hair was short – _yes, wonderful_ – and a little paler than he was used to. There were noticeable wrinkles around his eyes, and the eyes themselves…

He was smiling. The same smile he’d given to Takaoka-sensei, approaching with steel in his hand. He could read the earnest bloodlust in his own features, clear as day.

“How old was I?” He asked, after he’d considered the picture for a while. He didn’t think he was any older than his mid-forties, but then, he’d always looked young. Maybe that persisted.

_“I can’t say.”_

“Figures.” He sighed, and looked up at Karasuma. “What about a picture of the research facility?”

She appeared to ponder the idea. _“I think that counts as classified information about the research, sorry.”_ She said, apologetically. _“Five more minutes until scanning is complete._ ”

“What about a picture of where I live?”

_“That’s the research facility.”_

Nagisa blinked. “I’m a _scientist?_ ” Even if he weren’t in the end class, it was not a profession he’d ever considered. He supposed he put more effort into his observations of Korosensei than anyone else did, but that hardly seemed a basis for a research career.

“ _That,”_ Ritsu said. _“Is-“_

“Classified?” He interrupted, resigned to the expected answer. She beamed at him. “Of course...I suppose we should just wait for the scan.” Karasuma nodded at him, wordlessly, and they dropped into silence. It would have been completely quiet if not for the noises outside – his classmates yelling in the distance, birdsong from the roof, an odd scratching at the walls…

Nagisa turned to stare suspiciously at the outside wall, below the window. He caught Karasuma’s eye and gestured minutely in the direction of the quiet sounds. The agent held the eye contact, followed it, and then inched quietly towards the window. He looked down.

A brief pause.

_“Get back to the field! No eavesdropping!”_ The sudden volume of his shout made Nagisa wince, glad that the headset covered his ears. He heard two voices screech a little in shock, and craned his head as best he could to see Maehara and Okajima fleeing in terror.

“…If they heard anything, they won’t keep it quiet.” Nagisa pointed out, a little wearily.

Karasuma breathed very slowly and deliberately for several seconds, irritation twitching his brow. “Ritsu, please let the students know that I’ll be briefing them later, and that information leaks aren’t to be tolerated. Be subtle.”

_“Yes, sensei!”_ She chirped, and then presumably followed his instructions. It was hard to tell, given that she remained precisely where she was on the phone’s display.

The remaining minutes passed quickly. Nagisa had never been so grateful for a beep as the one that sounded from the headset, directly before the neck brace released him. His hand went up instantly, touching lightly at the skin of his throat. “Can I take it off?”

_“Yes._ ”

He didn’t wait for further instructions, pulling the thing off. His hair had become sweaty and unpleasant, sticking to his neck. There was also a small smudge of blood on his finger when he pulled it away from the injection site.

“So, how long will the procedure take?” Karasuma asked while Nagisa set to work tying his hair back up. There was a dull ache where the needle had been.

Ritsu hummed. _“Including rest cycles, it will take six days.”_ She said. _“After that, you will be able to remove the headset. However, it is likely you will need a further recovery period of at least two days.”_

Nagisa grimaced. “Finals are only weeks away…”

_“If this works, Nagisa-kun, you will easily get the best mark in a number of things. If nothing else, you are fluent in English._ ”

Karasuma raised an eyebrow. “Useful.” He commented.

“Well, that’s a definite benefit.” Nagisa murmured. “How can we do this, sensei?” He put the headset carefully back into its case, and stood up with his phone.

“…It might be difficult.” He said. “Depending on how often you need supervision.”

_“If you make sure to keep your phone charged, Nagisa-kun, I can try to remind you of when to take your medication. And I can call people if you need outside help.”_ Her avatar looked towards Karasuma. _“Sensei, could you supervise Nagisa-kun during the active modification cycles?”_

“How long are the active cycles?” He asked.

_“Five hours. With twelve hour recovery before the next active session.”_

Karasuma held his hand to his mouth, brows furrowed in thought. “If he stays at my house, I can supervise evening and night cycles. Anything else, though…”

_“Aa.”_ Ritsu nodded. _“It will have to do. Maybe the rest of the class can help?”_

Their teacher grimaced. “And then I’ll have you all knowing where I live. Lovely.” Taken aback at the sardonic almost-humour from such an unlikely source, Nagisa let out a surprised laugh. “At any rate, if we’re going with the idea that Nagisa will vanish for a week, what will the story be when he returns?”

“…If it’s anything traumatic, my mother might not react well.” Nagisa admitted. “Even without that…I don’t think she’ll let me out of her sight for a while.”

_“You can always pretend amnesia.”_ Ritsu pointed out. _“It’s difficult to disprove, and if we let you reappear while you’re still recovering, there will probably be symptoms to support the idea of head damage.”_

“Then I’ll be stuck in hospital for ages.” Nagisa pointed out, grimacing at the mention of ‘head damage’. “The bills will be horrible.”

“Well, we’ll have time to figure it out.” The assassination instructor decided. “For now, we should brief the rest of the class quietly, and arrange a way for you to disappear.”

“Are we telling Bitch-sensei?”

Karasuma grimaced. “If necessary.”

_“Sensei, I can use the students’ phones to tell them what’s going on.”_ Ritsu offered.

“That’s probably the most secure way to do it. Thank you, Ritsu.”

“…I usually walk home, so if I leave late tonight from after-school lessons, it could be believable for me to disappear on the way home.” Nagisa mused.

“Hm.” Karasuma considered his words, his near-perpetual frown light and thoughtful. “I drive, so I’ll get back first. I’ll cover my license plates, disguise myself, and then drive to abduct you, and take a very circuitous route home. How does that sound?”

“…Terrifying, sensei.” He replied, quite honestly. He wondered whether being able to make abduction plans on the fly was a special forces thing, or just a Karasuma-sensei thing. He had very little idea what the man had done for a living before this, after all.

“Then it’s settled. I’ll put the case into my car until then.” Karasuma nodded decisively. “You should return to class, Nagisa-kun. Perhaps try to kill the octopus when you arrive.”

_“I’ll coordinate with him, sensei.”_

The two of them who were not artificial intelligences blinked with surprise as the middle panel of the case, as well as the locking panels, closed on their own with a few whirrs and clicks. The older man shrugged, and bent to pick the case up, utterly ignoring the wheels. Nagisa took a moment to feel jealous of his obvious strength.

“I’ll see you later for after-school lessons, Nagisa-kun. Ritsu, try to brief everyone discreetly.” He nodded to them, and left the room.

Nagisa looked down at his phone, feeling quite overwhelmed. “…Alright, what now?”

_“Now, I prepare my fixed artillery body, and you prepare your knife._ ” Ritsu said. _“I have enough experience shooting at beings like sensei that I should be able to score some hits if you distract him.”_

Back on the reassuring ground of sensei-killing, Nagisa felt some tension leave his shoulders. “That sounds good. Can you give me any tips?”

She giggled. _“Nope!”_

“Naturally.” He sighed at her, slipping her into his pocket. “Alright, I’ll try to get him when I apologise for missing class. Please be ready to support me with your guns.”

_“Of course!”_

\---

Naturally, he did not succeed at killing Korosensei.

Ritsu did hit two tentacles, though, so he counted it as a minor victory.

**Notes for the Chapter:**

> Helloo. I'm taking a pop at the time travel trope. This was posted on tumblr first, and very minor edits have been made for this edition. Tumblr will likely remain one chapter ahead at all times, and chapter 2 is in fact live on tumblr now. My tumblr is tenspontaneite.
> 
> Feedback shall be greatly appreciated, as these characters are new to me and I do not know their ways.


	2. Chapter 2

**Summary for the Chapter:**

> Nagisa has himself abducted.

Nagisa spent the rest of the day fretting quietly about his impending abduction. It turned out he needn’t have worried; it went off near-flawlessly.

He hadn’t quite managed to be as relaxed as he usually would have been on his walk home, and so he was on edge enough to notice the sound of a car stopping ominously close, out of sight in the evening gloom. Not-expecting-abduction-Nagisa wouldn’t have paid that any particular heed, though, so he kept walking with barely a glance in its direction.

He thought that, even without expecting anything, he would have been vigilant enough to notice the footsteps coming up behind him, so he allowed himself to walk a little faster. He watched shadows in the street-lights, observing the warped shadow of a taller person falling in line with his, uncomfortably close, and looked over his shoulder-

Not-trained-in-combat-Nagisa wouldn’t have known what to do about the hand which closed over his mouth, or the powerful arm that wrapped around his throat. “ _Mmmrph!_ ” He made a shocked sound into his assailant’s hand, as he might have if genuinely surprised by this, and struggled as he was pulled into a choking grasp. It was difficult deciding how to struggle. He thought that he might be able to wriggle free by elbowing his assailant in the floating ribs if this were real, but he also wasn’t sure if that was something non-combat-trained-Nagisa would think to do. He went for it anyway, more weakly than he could have, and found the attack utterly ignored. Of course. He spent the following seconds flailing ineffectually and waiting for chloroform.

He’d helped Okuda make some in the lab before, with Korosensei’s supervision, so he wasn’t unfamiliar with the scent of it. He’d never had the knock-out concentration shoved in his face before, however, so he took several seconds to marvel at how much more potent it was. In the seconds after that, he didn’t really have the capacity to marvel at anything, and he was quite promptly rendered unconscious.

\---

Nagisa woke in a comfortable armchair with a mild headache and lingering dizziness which could be attributed to the chloroform.

_“Ah, you’re awake!”_ Ritsu’s voice exclaimed. He looked over and found her on his phone, which was sitting on a dark wood coffee table, along with a glass of water. _“Good! I’ll let Karasuma-sensei know.”_

“Ritsu.” He slowly straightened in the chair, finding himself in perfectly good condition. “I suppose there were no problems, then?”

_“Well, we think that someone saw Karasuma-sensei taking you, so your abduction might end up on the news.”_ She said, matter-of-fact, as though this wasn’t a potentially mortifying piece of information. _“But it hardly matters, since Karasuma-sensei left no evidence.”_

Nagisa stared incredulously at her. “It matters to me!”

Phone-Ritsu waved her hand dismissively. _“Ah, this is nothing. Even if it does end up on TV, you’ll have memories of much worse soon._ ” Her eye gave off a deliberate glint. _“Imagine how it would be if everyone found out that class E were Korosensei’s hostages, and the press were all following you around trying for interviews. Wouldn’t that be so much worse?”_

“That…isn’t reassuring.” He managed, desperately hoping that such a situation was hypothetical. “Did that really happen?”

She smiled. It looked quite similar to one of his own, actually – she was much better at facial expressions now. _“I couldn’t possibly say!”_ He glowered at her, which only seemed to make her preen.

“Nagisa-kun.” A familiar voice cut in, Karasuma stepping forwards from the left-most door. “How are you feeling?”

“Ah, Karasuma-sensei.” Nagisa blinked owlishly at him. “I’m fine. Only a little headache.” He paused, and added “You kidnapped me very well. I couldn’t do anything.”

A slightly sour look came upon the man’s face. “Aa. Well, I never thought I would have to train you all against kidnapping attempts, which might have been overly optimistic of me.” A brief silence. “You might have been able to get free if you had been truly trying.”

Nagisa dipped his head, a small smile pulling at the corners of his lips. It was nice that his instructor had noticed. “I didn’t want to seem too good at fighting, just in case there were witnesses.”

“Good judgement, especially considering there was at least one witness.” Karasuma sighed at that. “Well, at any rate, there weren’t any better moments, so I suppose we’ll just have to deal with the fallout as necessary.” He gestured abruptly towards the glass of water. “You should hydrate now. I’ll get you some food.” Without any further word, he turned and headed back through the door he’d come from. Now that Nagisa was paying attention, he could smell food.

_“Karasuma-sensei is very considerate.”_ Ritsu chirped. _“While you were unconscious, he visited a store to stock up on rations for you. He even bought some multivitamins, which will be a real help!”_

Nagisa smiled in the direction of the door. “Karasuma-sensei is quite a considerate person.” He agreed, reaching out for the glass of water and taking a long gulp. “…have you spoken to the rest of the class, yet?”

_“I have. Once they were off the mountain and Korosensei was far away enough, I spoke to them all using moving text on their screens so no one would hear anything, or have any evidence for police to find._ ” The pink-haired avatar seemed exceptionally cheerful at that. _“They’d been gossiping, of course. By the time I spoke to them they’d all heard that a time-travelling scientist had sent the case to you. I told them all that you would be taking on an experimental procedure to help you learn lots of new information very quickly, which is of course true.”_

He took a moment to absorb that, draining a little more of the large glass. “So, you didn’t tell them that it was me who sent the case?”

_“I didn’t even confirm the time-travel part. It’s best if some people don’t find that out before you can control their reactions.”_

Nagisa stared at her. “That sounds a little ominous.”

Ritsu pouted. _“It might be. We also decided that anyone who ends up helping you during this will have to be the people who sometimes skip class. Karma-kun, of course, along with Terasaka, Yoshida, and Muramatsu. Students like Nakamura, Maehara, and Okajima, for whom it wouldn’t be out-of-character to skip, will also be in rotation.”_ After a pause, she continued _“Of course, you might not end up needing supervision. Sensei has given me access to his security cameras and security system, so we might be secure enough._ ”

“…He has security cameras?”

_“And a secret escape tunnel! That’s how he brought you in._ ”

So, Karasuma-sensei was quite paranoid about his security? It fit him. Nagisa wasn’t very surprised. “Will the others be coming that way, if they have to?”

_“…Probably? It could be bad for Karasuma-sensei’s image if his students are seen visiting his house._ ”

“I would rather not end up with that sort of gossip, no.” Their instructor confirmed dryly, reappearing with unsettlingly impeccable stealth. Nagisa controlled his reaction and did not startle, looking up from the chair. His abductor and host had returned with a bowl and chopsticks in hand, as well as…pills? “Here, Nagisa-kun. Some vegetables with rice, and some multivitamins. Ritsu claims they will be useful for keeping you healthy and assuring a swift recovery.”

“Thank you, sensei.” Gingerly, Nagisa took the bowl, and then the chopsticks and pills. He settled the bowl in his lap and inspected the two white pills. “I thought you were only meant to take one a day?”

_“The extra nutrients will likely be needed, Nagisa-kun._ ” Ritsu informed him, almost apologetically. _“That’s why your dinner is quite big today. If you have difficulty keeping food down over the next few days, it will be best for you to have started off well.”_

Nagisa blinked, wordlessly downing the pills with a quick gulp of water. “I might have trouble keeping food down?” He asked, taking his chopsticks in hand.

Karasuma-sensei settled into a chair beside his. “Ritsu claims that you’re likely to run a fever, and probably experience nausea. Apparently, despite the immunosuppressants, your body is still likely to react to the procedure negatively.”

He nodded slowly, making a start on his uncomfortably large portion. He swallowed a mouthful of rice. “Ritsu-san,” He said, gathering another clump of sticky rice on the ends of his chopsticks. “Now that I’m here, and it’s too late for me to back out, can you tell me more about the procedure?”

Before Ritsu could answer, Karasuma cut in. “Depending on how weak your stomach is, you may want to wait until after you’ve eaten.” He said, forebodingly. Evidently, he’d learned some of the details.

Nagisa looked despairingly into the bowl, and nodded. “…Aa.” Quietly, he set to work on his dinner, and didn’t ask for more information.

\---

Karasuma-sensei had quite a nice house. It wasn’t very traditional, except for the presence of a kotatsu in the sitting room and a house shrine in one of the halls, but the comfortable chairs and dark wood furniture everywhere made for a very pleasant effect. Nagisa refrained from asking or commenting about anything, though – Karasuma-sensei was a very private person, and he probably wouldn’t appreciate it. Nagisa was grateful enough to the man for opening his home to him for this.

“To limit the amount you’ll have to move during this all, I’ve moved the spare futon downstairs for you.” Karasuma explained, showing him around the downstairs of the house. “That way you can get to the downstairs bathroom, and the kitchen, without having to use any stairs or having to walk very far.”

Nagisa nodded mechanically through all of the demonstrations and explanations, feeling quite overwhelmed by the care being taken for him. His instructor was going to such an effort for him, on such short notice, and…well, he wasn’t used to that sort of consideration. It was only Korosensei, and now Karasuma-sensei, who had gone to such trouble to support him. He wasn’t sure what to say.

In the end, once his host had shown him where all the food was in the fridge, and explained the locations of the bottled water he was expected to keep at the bedside, Nagisa only said “Thank you, sensei.” There was an extreme of gratitude where it became difficult to say much more, and he’d reached it.

Karasuma, a direct man who didn’t speak unless it was for a useful purpose, seemed to understand well enough. He inclined his head, expression softening very slightly. If Nagisa were slightly less observant, he might have missed the edge of sympathy.

The sympathy was sort of warranted in this case.

“Since you won’t have the chance to for a while, please feel free to take a shower.” He said, having already explained where the towels and soaps could be found.

Nagisa nodded. The headset, after all, was a very advanced piece of technology, and wouldn’t do well if doused in water. As such, he wouldn’t be able to wash his hair or scalp until the procedure was finished. “I think I will, sensei.” He accepted politely, and was promptly left to it by his very accommodating instructor. He returned to the bathroom, sans Ritsu-phone, and swiftly located a towel and the antibacterial soap that Ritsu had recommended.

It always felt weird to shower in unfamiliar places, but Nagisa had more than enough to distract him. Ritsu had explained everything he could expect for the procedure, and he fully understood why she’d waited until now to do so. He wasn’t sure he’d have had the nerve to go through with it otherwise.

The headset, as it happened, would be drilling into his spine. There, as well as into his bloodstream, it would inject highly sophisticated nanomachines and chemicals that, in concert with the signals put out by the headset, would essentially rewire his brain. Since there wasn’t room in the case for a full-body manipulator, what the nanomachines could do in his spine was limited, so his nervous system would end up out of whack with his brain. As such, he could expect to have difficulty coordinating his body and moving as he intended for a while after the procedure.

It was the chemicals, as opposed to the nanomachines, that his immune system was likely to object to. Even with a lessened response, the treatment would likely make him feel quite ill. He was to expect fever, nausea, and probably delirium. These were among the least of the side effects he might experience, however.

During the five-hour active cycles, Nagisa would be unconscious. The headset would be inducing partial paralysis to prevent him from moving and potentially disrupting the treatment, which was a very unpleasant sensation. In addition, the active neural rewiring would apparently cause an exceptionally unpleasant headache, with the potential for severe phantom pain throughout his entire body. Nagisa didn’t technically have to be unconscious for the active cycles, but given the pain and the paralysis, it was certainly for the best.

Even during the recovery cycles, things would be unpleasant. For one, the pain would linger, though the medication ought to mitigate that. Since the procedure was a process, he was likely to be exceptionally confused and uncoordinated. He might have difficulty reconciling different timelines, experience powerful flashbacks, or any manner of memory-related symptom. Due to the differing capabilities of his future and current bodies, he was also probably going to have difficulty integrating sensory information for a while, and might experience periods where he didn’t have control of his body at all. Ritsu’s main concern was that he might either be too incoherent to care for himself, or that he would be physically incapable of it.

If at any point he showed himself as unable to take his medication, the classmate skipping schedule would be implemented. In the interests of Karasuma’s privacy, Ritsu wouldn’t be telling any of them where to go unless that became necessary. If asked about their absence, they’d admit to looking for Nagisa, which was a perfectly reasonable thing for fellow assassination classmates to skip class for. Korosensei would probably approve.

And…there was the thing. The main potential point-of-failure.

Nagisa stepped out of the shower, pulling the towel to his skin. The only hairdryer Karasuma owned was a tiny travel-sized thing, which was probably sufficient for short hair, but would be a pain for his. Still, he couldn’t afford to get water in the headset, so…

Sighing, he set to work thoroughly drying his long hair, all the while hoping that none of his classmates would give the game away. Surely, no one would expect Karasuma-sensei to do any abducting, right? He should be the last suspect on anyone’s mind. But, then again, Korosensei was very sharp, even if he didn’t tend to show it. If the members of class E gave any indication, he _would_ notice. And besides that, his sense of smell was very acute. Karasuma would be doing his best to account for that, but even so…

It was quite late by the time he finished drying his hair and dressed again, leaving the bathroom with fluffier hair than he was used to, since he didn’t tend to use a hairdryer often. It tickled at his neck as he walked through the hall to the sitting room he’d be spending most of the next six or more days in, finding Karasuma-sensei waiting in an armchair.

“You’re done. Good.” The man said, in lieu of a greeting. He stood and presented Nagisa with a pair of elastic bands. “These aren’t the best thing to tie hair with, but there’s no metal.”

_“Make sure not to tie it up like you usually do, Nagisa-kun. Your hair shouldn’t be too thick on your skull, if possible.”_ Ritsu informed. _“Keep it clear of the back of your neck, too. It could obstruct the spinal taps, otherwise.”_

Nagisa inspected the bands, running through options in his mind. He sighed. “So, basically, pigtails.”

_“Or twin braids. That would definitely keep it out of the way._ ” The avatar nodded brightly.

He made a face. “Couldn’t I make a single braid, and just push it to the side?”

Ritsu pondered his query for a very brief second. _“That could work, yes!”_ She agreed, and promptly disappeared from the screen. What appeared was a step-by-step animated diagram of how to braid one’s own hair. He stared at it in mild terror, never having attempted anything of the sort before. “…”

_“It’s easy! Just follow these steps!”_ Ritsu encouraged.

Nagisa exhaled, and then reached for his hair. “Show me from the beginning, Ritsu-chan?”

_“Of course!”_

Following her directions, he managed to wrangle his hair into an uneven and messy plait, tying it at the end with one of the elastic bands he’d been provided with. Ritsu provided him his reflection through use of the front camera of his phone, and he concluded that it didn’t look as mortifying as pigtails would have…but he still sincerely hoped that neither Karma nor Nakamura would end up having to come help him. They’d certainly take pictures. “This will do, I suppose.”

Karasuma might have looked vaguely amused. It was hard to tell on him – he seemed to entirely lack a sense of humour, most of the time. “Are you ready to begin?” He checked his watch. “It’s almost 1am.”

Nagisa grimaced, and flipped the braid around down the side of his neck. He most certainly was _not_ ready, but he doubted he’d ever be more prepared. “I am.” He lied, calmly, and approached the large time-travelling suitcase that was situated a short distance from his futon. He opened the first lock, but when the panel sprung up, the second stayed in place with his fingerprint. He frowned. “Ritsu?”

_“Sorry, now that the case has been opened once, additional security protocols are in place. Different compartments now require a code to open, which changes every 20 seconds. Please type the following numbers: 2, 6, 7, 2, 1, 4, 6, 9, 0, 5, 6, 7, 9, 0, 3.”_

He jabbed at the number keys quickly, the fifteenth digit causing the lock to release so quickly that the compartment lid almost smacked him in the face. It seemed like a fairly good system – without being in communication with Ritsu, there was no way that anyone could get into the suitcase, and she was probably too advanced for anyone to hack at this point in time. Fifteen digits was also too long for anyone to discover by trial and error in twenty seconds, even assuming Ritsu didn’t take offence at the attempts and detonate the case. His future self hadn’t been messing around.

Nagisa wondered, taking the headset in hand, what else he’d put in here, for it to be so ruthlessly protected.

_“Once a day, the headset’s supply of the nanomachine-chemical mix will need to be refilled from the bottles._ ” Ritsu explained as he removed all of the bottles and cylinders. _“You can do it yourself, even with the headset on, but it might be easier for Karasuma-sensei to do it when he’s home._ _It’s important to make sure it doesn’t run out during an active cycle, as nanomachine levels may need to be adjusted quickly during this time.”_

“I can take care of that.” Karasuma acknowledged. “How do I do it?”

_“On the left side, there is a hole with a small light above it. You inject the solution into the hole using the syringe until the red light turns green. It will need filling first-thing.”_ Karasuma, following her directions, took the bottles and syringes from Nagisa, also relieving him of the cylinders. As though anticipating another question, Ritsu continued. _“Nagisa-kun, you should take your painkillers twice a day, at least six hours apart. I will remind you if you forget. Your immunosuppressants should be taken once a day, with food.”_

“Then, I can help with the immunosuppressants as well.”

“Thank you, Karasuma-sensei.” Nagisa murmured, in what was beginning to feel a hollow expression of gratitude. All this effort, being put into his care…he would need to get a gift for the man to thank him, afterwards. After a pause for hesitation, he put the headset on, pulling his braid out of the way of the neck brace. “Should I press the button now?”

_“Pressing the button will engage the neck brace, and also make the helmet fit itself on. I have full control of the headset and won’t begin the cycle until you’re all ready.”_

He took that as a ‘yes’, and reached up to press the button on the middle of his forehead. The neck brace twined around his throat, the two sections sealing together, and he pulled stray bits of messy hair out of it while it undulated unsettlingly into the right fit. He took a deep breath, and lowered himself into the futon, feeling the inside of the headset swell against his skull.

The headset would tap his spine at the base of his neck and the base of his skull. Both of these places couldn’t have too much pressure on them, so he had to lay on his side, the weight of the headset carefully supported by numerous pillows. Feeling tense and awkward, Nagisa positioned himself how he’d been told to, and looked to the side.

_“Nagisa-kun. Can you reach the water bottles?”_ Ritsu asked, as Karasuma put her on the floor a short distance away, beside the three bottles of water that had been left there.

He reached out, and found he could easily grasp both the phone and the bottles. “It’s fine.”

Karasuma put three cylinders beside the phone; one plastic, two metal. “It seems the immunosuppressants are in red and yellow capsules, while the painkillers are in blue capsules.” He informed. “They should be easy to tell apart. Can you take them from this position?”

Nagisa took a bottle of water, opened it, and swallowed experimentally. “I don’t think so.”

“Then sit up. You can take your first pills now.”

He did as directed, accepting a single red-and-yellow capsule first and swallowing it down, followed by the blue one. They were both quite sizeable – he didn’t think he’d had to take such large pills before. “Anything else?”

“Hold still while I inject the solution.” Karasuma opened one of the metal bottles. It had the sort of nozzle which wouldn’t spill if knocked over, and a very small opening. Nagisa watched as he poked the needle through and pulled on the plunger, a pale yellow fluid filling the syringe. He kept unmoving as his teacher located the area on the left side of the headset, injecting it apparently without fuss. He did this twice more before the headset was satisfied.

_“That’s enough to fill it, sensei.”_ Ritsu said, quite professionally. _“Nagisa-kun, we can begin now. Please lay down.”_

Nagisa breathed past his nerves and, wordlessly, obliged. Once he was carefully situated on his right side, as comfortable as he could manage, he said “Is this okay?”

_“That’s fine, Nagisa-kun. The headset will electrically stimulate your brain to induce unconsciousness soon. After that, you will be immobilised, and your spine will be tapped. In around twenty minutes, the active cycle will be ready to begin. Once the cycle is complete, the spinal taps will remain, and the muscles in your neck will remain stiff to prevent movement, so please don’t be alarmed when you wake.”_

Nagisa peered, as best he could, at her avatar. He thought she seemed a little anxious. “…You’re not sure whether this will work, are you?”

There was a telling pause. _“It should, but we can’t guarantee it. There’s lots of data taken from all sorts of patients, and I’ll be directing the process every step of the way. But we can’t guarantee anything.”_

A highly risky experimental procedure, to be sure. Even though he felt sick with fear, Nagisa refused to let it show. He went carefully, calculatingly blank, staring impassively at Karasuma-sensei as he kneeled down to look him in the eyes.

“Good luck, Nagisa-kun.” His teacher said, serious and solemn. “I’ll be here when you wake up.”

He exhaled. “Thank you, sensei.” A pause. “…Do it, Ritsu.”

There was a slight, sharp pain in his head-

\---

_“-any minute now, since I’m no longer forcing unconsciousness. With luck, the painkiller will be effective enough that he doesn’t feel the spinal tap too badly.”_

“And his mental state?”

_“…Impossible to say, sensei. He’s one-sixth of the way through the active changes, but…”_

“I see.”

The voices were quiet, and both of them familiar. Each word throbbed like agony in his head, overwhelmingly familiar. Why did everything _hurt?_ When was the last time he’d been in this much pain?

_“…Scans indicate he is regaining consciousness. Nagisa. Please respond.”_

The name drew him from a pained stupor, just enough for him to open his eyes. As soon as he did, he regretted it – the light made pain flare through his head, dizzyingly, sickeningly intense. He closed them again. “…Ritsu?” he croaked, and…what was wrong with his voice? “…Ritsu. What...what’s wrong with me?”

_“You are wearing the neural reprogramming headset, Nagisa. One sixth of the changes have been made. What do you remember?”_

He…remembered…

What?

He couldn’t think.

“… _Nagisa?_ ” She sounded worried. “ _Can you open your eyes?”_

The light hurt. But pain was only pain. Pain was trivial. Nagisa opened his eyes, light distorting horribly through the blaring agony it induced in his head. He saw a floor, with an array of objects. A phone with Ritsu on it, stood up against a bottle of water. There were several bottles of water. There were also several medication cylinders which he remembered filling.

There was also a man. Too young, and too alive.

“…Karasuma?” He murmured, squinting through the visual distortion. The man remained.

“Yes, Nagisa-kun. How are you feeling?”

Nagisa stared through half-open eyes. “…Horrible?”

“Can you sit up?”

He blinked. Of course he could sit up. Why would anyone think otherwise? He…

He couldn’t sit up. Why?

There was the intention to sit up, he tried to do it, but…it didn’t happen. “I don’t think I can.” He murmured, quite distraught at the realisation.

“ _Can you move your fingers and toes, Nagisa?”_

He could see a hand in front of him. It was oddly smooth-looking. He concentrated, and the fingertips twitched, curled inwards. The grip was too weak. He couldn’t see his feet, but he could…feel? He could feel them. The toes moved when he tried to move them, he felt them curling over fabric. His fingers curled on fabric. The texture, the _feeling-_

“I can.” He said.

“I’ll help you up, Nagisa-kun.” A man said, reaching forwards. Nagisa looked at him in alarm, identifying his features with disbelief.

“Karasuma?” He blurted, headache pounding in his ears. “Is that you?”

“…Yes, Nagisa-kun. You asked that a minute ago.” He looked concerned. Nagisa had seen a lot of Karasuma being concerned, it had been a frequent state of being for the man. “Do you not remember?”

“Remember what?” He blinked, and saw Karasuma-sensei. He glanced around, finding his hand splayed out in front of him, his phone propped up with Ritsu looking out of the screen, and all of the things that had been laid out before he was knocked out. “…Karasuma-sensei?” He questioned, discovering worry in the lines of his face, and wondering at it. “Did something go wrong with the procedure?”

Karasuma looked at the phone, and she spoke up. _“…I don’t think so, Nagisa. You’ve been showing a degree of confusion and mental incapacitation which is probably to be expected at this stage. While you’re still lucid, please eat and drink something.”_

His instructor leaned forwards to help him up. Nagisa wasn’t sure why, until he discovered that he couldn’t sit up on his own. “…Sensei. I can’t sit up.” Panic crept into his voice, no matter how he tried to hold it back.

“I think that’s normal, Nagisa-kun.” The man said, solemnly, holding out a bottle of water as he held him up by the shoulders. Nagisa reached out and closed his fingers around the bottle, weakly, finding that his neck was too stiff to move. But, Ritsu had told him about that, hadn’t she?

Carefully, he opened the water and drank, as much as he could. He put the lid back on the bottle and looked at it, bizarrely confused by the sight of it, the bottle two-thirds empty. His fingers were wrapped around the plastic and it felt…not right. It was smooth, a little cold, and the sensations were far too simple. He tried to flex his spine and nothing happened.

“You should take some vitamins.” A familiar voice said, and Nagisa looked up. It…looked like _Karasuma._

“Karasuma?” He said, disbelievingly. “But you’re dead.”

The man’s eyebrows went up, something like shock flashing over his face. “…I’m perfectly alive, Nagisa-kun. You’re very confused at the moment.” He said, and held out two white pills. “Please take these.”

Nagisa accepted the pills into his hand, but couldn’t stop staring. “I’m quite sure you’re dead, Karasuma.” He argued, knocking back the pills. The taste of them was…simple. Dull. He could barely smell anything, either.

“I am not dead, Nagisa-kun.” Karasuma informed him, holding out…a cereal bar? He hadn’t seen that brand in _decades._ And since when did anywhere still manufacture this sort of thing, anyway?

“I’ve not had a cereal bar since I was….forty? Fifty?” Nagisa muttered, immensely confused, as he accepted it. He opened it and confirmed that it was, in fact, a cereal bar. It tasted like he remembered cereal bars tasting, too. He inhaled the thing, suddenly ravenous, and looked up.

“There’s more if you want.” Not-dead-Karasuma claimed, and made good on his word. Nagisa snatched it eagerly, fingers feeling too-solid and too-weak around its plastic wrapper.

He put one wrapper aside and opened another. He took one bite of the cereal bar, and was chewing through it when he noticed the hand supporting his shoulders. He looked up, blinking. “Sensei?”

Karasuma-sensei seemed worried, still. “Nagisa-kun.”

“When did I wake up?”

_“About five minutes ago.”_ Ritsu answered for him. He looked over to find her on his phone, propped up by a bottle of water, the charging cable connected. _“You’ve been confused and disorientated enough that it might be best to put you out for another few hours.”_

Nagisa blinked, finishing the cereal bar. He politely put the wrapper aside next to another one he didn’t remember eating. “That’s a little unnerving.” He said, certain that he’d ordinarily be very worried over not remembering the last five minutes, but…it was hard enough to concentrate, let alone worry.

“You’ve eaten, had some water, and taken some vitamins.” Karasuma informed him. “I have to leave for the satellite campus soon, so I won’t be here the next time you wake up.”

“…Okay?” He offered.

“I’ll help you back down.”

Nagisa observed as he was lowered carefully down onto a futon. “Thank you, sensei.” He said.

“You’re welcome, Nagisa-kun.”

\---

_“Nagisa? Can you hear me? Are you awake?”_

Nagisa was in a lot of pain. Pain could be dealt with, though. It could be ignored. “…Ritsu?” He inquired, opening his eyes. “What’s going on?”

_“This is the second time you have woken since your first active neural reprogramming cycle. You should drink some water, and take your painkiller. Can you sit up?”_

He could feel his back, feel the muscles in it, but they…they weren’t right. He tried to flex his spine and couldn’t. He tried to extend and nothing happened. “It doesn’t feel right.” His arms felt different, too, but less so. He moved the hand he could see in front of him and used it to push himself up. “What’s wrong with my back, Ritsu?”

_“It’s a normal human back, Nagisa. It will probably feel very strange for a while._ _Please take your painkiller.”_

Nagisa blinked, absorbing her words, and looked at the pill cylinders he’d assembled. He reached for the nearest and found the blue capsules in it, extracting one and swallowing it dry. He finished off a bottle of water for good measure. “I’m…part way through the neural reprogramming. Aren’t I?”

Ritsu brightened. _“You are. Are you feeling more focused now?”_

“I…think so? Was I not, before?”

_“You woke up earlier today and couldn’t keep your memories consistent. I think it’s normal._ ”

“Things feel disconnected.” Nagisa murmured, finding that his headache became blinding when he tried to remember specific events, or how he’d got here. He looked at his hands – the right size, but too young. He slowly, carefully, engaged the muscles in his abdomen, marvelling at the odd rigidity of the flesh. “This feels _weird_ , Ritsu. I think I’d like to be knocked out, now.”

_“If you like, Nagisa. Please lay down again for me.”_

He settled into the futon and waited for unconsciousness.

\---

“Karasuma?” he blinked up at the man. “Aren’t you dead?”

His dead former instructor sighed at him.

\---

Nagisa became most lucid, coincidentally, not too long before he was due to go under again. “I kept forgetting things, didn’t I?” He commented, a bowl of stir fry in his lap, on the futon.

“You varied between being convinced I was dead and being your…base self.” Karasuma confirmed, eyes quite focused on him. “Are you feeling any better?”

He chewed and swallowed a mouthful of food, torn between sensations. On one hand, it tasted good, and satisfying. On another, the texture and taste both seemed oddly flat, as though muffled by a cold. “I’m less confused, at least.” He looked up, uncomfortable. “Sensei, I think I remember you being dead, in the future.”

“I did guess, by the third time you told me I was dead.” The man remarked dryly.

“Did I say anything else?” Nagisa asked, collecting a clump of noodles and vegetables onto the chopsticks. His fingers felt brittle and rigid, his skin…dull. Textures didn’t feel right. “I can remember some things, but none of it is…I’m not sure.”

_“The brain is very complex, Nagisa. Until everything is finished, nothing will be seamless.”_

“It won’t be seamless even then, Ritsu. I was there for the planning.” He retorted, and blinked. “…Hm.”

Karasuma lifted an eyebrow. “You remember?”

“A little.” He took another mouthful, intent on the wrongness of his senses, the strangeness of his flesh. He swallowed, and said “I think my body was very different, in the future. Everything feels _wrong._ ”

“You _did_ mention being forty or fifty as though it were a long time ago.” Karasuma pointed out. “You must have been quite old.”

Something about the statement felt off, but it was also true. “Aa. I was old.” He glanced at his phone. “Can’t you say how old I was? I’m already under the procedure.”

Ritsu giggled, secretively. _“That wouldn’t be as fun.”_ She claimed cheerfully.

Nagisa finished off his dinner and rubbed at his face. “If you say so.” He sighed, and carefully tried to stand up. He had to think about every part of the movement. “Do you think this difficulty with my body will get better?”

Ritsu frowned. _“Ah…no, it will probably get worse.”_

Nagisa grimaced. “Ah. Well…” He handed his bowl to Karasuma, bowing slowly. “Thanks for the meal, sensei. Sorry for not helping.”

“You’re basically undergoing brain surgery, Nagisa-kun.” The man commented, unperturbed. “I don’t expect you to do a single chore while you’re here.”

He bowed again, grateful beyond words. “…I think I’m going to go to the bathroom, before I go back under.” He said, feeling distinctly unwashed and in need of the facilities. “I won’t be long.” He walked unsteadily down the hall, finding the correct door and setting to work with his sponge bath.

Nagisa stared at himself in the mirror, the sight of the headset unbelievably strange. Its dark metal looked distinctly like something from science fiction, especially with the brace wrapped around his neck. A brace which made it quite difficult to wash properly, since he couldn’t move his head or neck much at all.

He finished eventually, drying off. He took a few moments to re-braid the exposed hair, slightly better at it with a mirror available. The dull pain of the spinal taps accompanied every movement.

Once finished, he got back into the same slightly smelly clothes and returned to the sitting room, bending carefully to take his immunosuppressant and painkiller. “More multivitamins, too?”

_“It’s a good idea.”_ Ritsu confirmed, twirling virtual hair around a finger.

Nagisa nodded, frowning as he tried to remember. “The nanomachines,” He murmured, taking two multivitamins in hand. “They’re…artificially producing medication, aren’t they?”

_“That’s right!”_ At Karasuma-sensei’s curious look, she elaborated. _“Most of the nanomachines are acting directly on the brain and nervous system, but some are manufacturing biological compounds that we couldn’t send through time, because they count as alive. For example, there are numerous drugs developed in the future to help the brain recover from injury, as well as things to help the brain form connections more quickly. They’re invaluable for the process!”_ She beamed. _“Those compounds are acting during the recovery cycle, helping to integrate the changes made in the active hours.”_

“So, I’ll be worst each time I wake from an active cycle?” He checked, receiving a nod. “Well, I suppose I’d best get to it quickly, in case there are any troubles in the morning.”

_“Do you feel ill yet, Nagisa?”_

He took stock of his physical condition, frowning. “It’s hard to say. I feel dizzy, and my head hurts, but I don’t feel nauseous.”

Karasuma extended a hand to his forehead, quite suddenly. The abrupt movement triggered a reflex that felt like it should have engaged his back, but nothing happened. Perhaps for the best; it didn’t feel like a very friendly reflex. “You feel a little warm, so perhaps the fever is starting to come on.” The instructor observed. “You might feel worse in the morning.”

Nagisa sighed, and nodded. Once the hand withdrew, he stood by to allow Karasuma to refill the nanomachine solution, laying down once he’d finished. “Goodnight, sensei, Ritsu.” He said, watching his host’s expression soften slightly again. Nagisa smiled, as always pleased to find signs that the taciturn man genuinely cared.

“Goodnight, Nagisa-kun.” Karasuma said, shortly before the headset engaged.

\---

“Calm down!” The man barked, as if he expected him to _listen_ , when he was saying it wearing _that face!_

Nagisa tried to reach out and strangle, tried with every limb, but only four responded. What had he been drugged with? Since when had anyone developed a drug that could take _him_ out? Since when were people sending _clones_ of his team after him, for god’s sake-

He cast his eyes around furiously, but didn’t find anything that looked like a weapon. The bottles were plastic or thin and metallic, the cylinders were worthless, there was…ah, _there-_

Nagisa’s hand shot out, far more slowly than it should have, and closed around a syringe. He lunged upwards, neck immobilised, but the rest of his slow, rigid muscles responding well enough as he forced them. He dodged under the arm that came out to force him down, fighting against a pounding headache and his vision swimming as he surged up, up, bringing his arm around-

A hand gripped his millimetres from victory, and Nagisa screamed wordlessly at him, furious and terrified and _enraged_ , his drug-induced weakness acting against him. He couldn’t even force a needle into a human man’s neck. What had they _given_ him?

“You’re not thinking clearly,” The impostor tried to say, pulling his wrist around into a lock that shouldn’t have worked. He was so _rigid,_ completely inflexible.

Nagisa bit back the things he wanted to shout at this horrible, abominable captor. He was captive, and weakened. Fine. There was no need to lose his mind along with his strength. He went pliant in the man’s grip, feeling subtly for weaknesses in the lock.

“…Nagisa-kun?”

He twitched, and kept calculatingly silent. He couldn’t hear Ritsu. He glanced around, finding the bewildering sight of an absurdly luxurious living room, and a futon, and a…

Nagisa frowned. A large metal suitcase, the middle compartment open and empty. He tried to twitch his neck, paying closer attention to the heaviness of his head, the feeling that his throat was wrapped around with something firm, and twin points of dull pain on the back of his neck…

A neural reprogramming headset?

He allowed his muscles to go lax, genuinely now, rather than as a ruse. “…Ritsu?” He called. Surely, if their plans had worked, she wouldn’t have allowed him to be undergoing the procedure without her supervision?

_“Nagisa! Are you finally listening to me?”_

His eyes followed the voice to an old mobile phone. Her avatar was on the front of it, looking somewhat panicked. “…Ritsu.” He said, quietly. “We made it?”

Her simulated features loosened into a sad, soft smile. “ _We did, Nagisa-kun. You’re a third of the way through the procedure.”_

Nagisa breathed, slowly, and allowed the syringe to fall from his hand. Cautiously, the man behind him released the wrist lock, and stepped away. Nagisa unfurled, orienting himself towards the spectre he’d thought a cruel weapon engineered specifically to destroy him. “…then, you’re Karasuma?” The thought curled, painfully, like a sickle between his ribs.

The once-head of the Ministry of Defence nodded. “I am.”

He looked at the futon, violently disrupted by the struggle, and bent to rearrange it. “I’m glad. I’m sorry for…that.” He wasn’t sure how he’d come to be here, or why he was being supervised by Karasuma when they’d expected to muddle through in whatever hole they could find, but he was grateful.

“It’s no problem.” The man watched him for several seconds. “Ritsu didn’t mention the possibility of violent delusions.”

Nagisa’s head dipped, troubled. “We weren’t aware it might get so bad.”

_“You should take your pills and such quickly, Nagisa-kun, in case you relapse.”_ Ritsu urged him, and he glanced over at the assorted cylinders.

“If it’s after an active cycle…the painkiller?”

“The painkiller, food, and water. And multivitamins.” Karasuma corrected.

Nagisa smiled, a little hollowly. “Of course.” He murmured, and reached out to begin. He swallowed down his painkiller with a gulp of the water provided.

_“We had planned for our classmates to help you through the treatment if necessary, but I’m not sure that’s safe anymore.”_ Ritsu fretted. _“If you react like that with one of them…”_

He grimaced, and nodded. He eyed the high-energy cereal bars that had been presented to him with a roiling stomach, and forced them down regardless. “Make sure to knock me out if someone vulnerable comes here.” He said, softly, as he laid himself down. “I won’t risk hurting anyone.”

“I’ll remove sharp objects from the area before I leave.” Karasuma stated, sensibly.

Nagisa looked around the room, as best he could from his position. “Good idea.”

\---

“I’m hallucinating.” Nagisa said, to himself, ignoring the pleas of what sounded like his friend. “Everything. It’s all a hallucination.” His vision tilted crazily and he gripped onto the edge of the doorframe to stay up.

_“There’s no hallucination, Nagisa! Listen to me, or I’ll have to knock you out!”_

“You’re not Ritsu. Ritsu wouldn’t need to use a phone to talk to me. You’re an imitation.” He pointed out, cold and calm. He was weak, and couldn’t walk well, and couldn’t use his abilities, but he wasn’t locked in. He wasn’t even _restrained._ It was laughable.

He had only to get out, get back to his base…

The place was structured like a house, wood floors and furniture everywhere, ludicrously opulent. It even had a wooden _front door._ He staggered for it, unwavering. Escape would be easy, if his captors had been so lax-

He stopped, seeing a glimpse of the outer area through a small window in the hallway.

It…looked…

The cruelty of the hallucination seized him by the throat. His head swam. Aware that he was about to lose consciousness, Nagisa lowered himself down into a favourable position for falling-

\---

“…Ritsu? Why am I in the hallway?” he called, not sure where she was. The reply came from down the hall.

_“You freaked out, Nagisa. Quick, get back to the futon, have some water. I don’t think you should be awake much today, you might damage the headset.”_

\---

When Ritsu woke him late on the second day, his thoughts were hard to keep track of. He’d spent the day vacillating freely between confusion, delirium, and violent hysteria. Or so he’d been told, when he asked why he’d been tied up.

“I’m sorry to treat you like this, Nagisa-kun.” Karasuma apologised, clearly troubled. “Ritsu woke you a couple of hours ago, when I got in, and I had to restrain you then.”

Nagisa’s fingers twitched in their bonds, tied behind his back at the wrists. He thought, heart sinking, of the violent rages that his mother was prone to. “…I don’t mind, sensei.” He said, finally. “Have I eaten yet?”

“No, nor have you taken your medication.” The man scrutinised him carefully. “We should get that done quickly, while you’re coherent.”

Nagisa nodded, resigning himself to the indignity of being fed, and watched his host get up and head to the kitchen. “...How is it going, Ritsu?”

_“The procedure is as expected, though your symptoms have been worse than we expected.”_ She replied, softly. _“I’m grateful to Karasuma-sensei. We were wrong – we wouldn’t have been able to do this alone.”_

He nodded, sighing. “Aa.” Well, at least chance had provided for them, for once. “Hopefully, the extra help won’t be necessary for much longer.”

\---

Nagisa woke to complete agony.

His _head_ , his _eyes_ , absolutely _everything –_ it-

He screamed, pain and fear seizing his thoughts and _strangling_ them, he couldn’t think, he couldn’t breathe, he couldn’t move-

…he, he couldn’t move, he couldn’t move, _he couldn’t move,_ why, why

_“Nagisa! Please, focus!”_

…Ritsu?

He closed his mouth, the only thing he seemed able to control, except – his eyes? He could open them – it was dark. Night time. The lights weren’t on. “…Ritsu?” He croaked. “What…?”

_“I woke you during your active cycle, Nagisa, I’m sorry.”_ He moved his eyes sideways, seeing her tearful avatar in the periphery. _“It’s…a bit of an emergency.”_

**_“KA. RA. SU. MA….!_ ”**

The sound of it could have brought the roof down, it was _loud._ Nagisa groaned, the sheer volume of it agonising. But, it was…who was it? It was…

Close by. _Familiar._

**_“_ I NEVER EXPECTED THIS FROM YOU, KARASUMA. _HOW DARE YOU?”_**

That _voice!_

“Ritsu…that’s…” He managed.

“It’s not what you think.” He heard Karasuma’s voice, sounding thin and brittle. Choked, even.

**“He’s a _CHILD!”_** The voice all but howled, rage and murder dripping from every syllable. He could see something dark writhing in the corner of his vision, long shadows whipping in the gloom.

He hadn’t heard that voice in a long, long time. Not outside of Ritsu’s recordings. He’d almost forgotten it. Except…of course he hadn’t, he’d only heard it a couple of days ago. Oh, he was confused.

“…Korosensei?” He asked, softly.

The movement of the shadows stilled. There was a harsh, heavy thump, and he heard Karasuma groan. The next second, there was a tall, tentacle super-being in front of him, the first there’d ever been. “Nagisa-kun.” Korosensei said, quietly, his voice rough with the angry colour of his skin. Nagisa looked up, as best he could, and saw his teacher lower himself down. His face was that black, angular rictus of fury that they’d only seen at especially dire times.

There was a flash of tentacles, and Nagisa experienced a brief rush of disorientation. Half of him was convinced he shouldn’t be able to follow their movement, but he _could_ -

He felt himself be lifted upwards, very gently, on a number of squishy limbs.

_“Sensei, please be careful! Don’t touch the headset!”_

“Ritsu-san.” Korosensei observed, turning his head to the side. “Are your parents involved with this? I thought you were defying them of your own will, now…”

“Sensei,” Nagisa cut in, voice weak. He hurt _so much,_ and it was _everywhere._ Still, he moved his eyes, looking up at his teacher as best he could. He smiled. “…It’s good to see you.” He was…dazed. What should he be doing? He exhaled, roughly, eyes stinging. He was…so, so very much in pain.

“I’m sorry I took so long, Nagisa-kun.” His colour lightened, slightly. A tentacle came forwards carefully, poking at the edge of the headset. Ah, that was right.

“Koro…sensei…” He struggled, unable to move anything except the muscles in his face. It was horrifyingly unnerving, but he had to defuse the situation… “Don’t remove it. It’s in my spine.”

The tentacles, which had been edging towards a lighter shade, immediately went inky black again. Korosensei’s next breath sounded like a hiss, like an angry snake. **“…I _see. Is. That. So?”_**

There was the sound of someone choking in the corner. Oh dear. “Ah, sensei?” Nagisa wished he could move. Then he could poke his angry teacher to get his attention better. “…Please stop.”

Black drained to yellow so swiftly it hurt his eyes. “Nyu – aaa, Nagisa-kun, I’m sorry!” Korosensei’s voice, suddenly shrill and contrite, made him wince. “Am I hurting you?! I’ll put you down immediately!” Abruptly, Nagisa found himself back on the futon, in precisely the wrong position. Nagisa became aware of a very not good feeling of pressure on his neck.

_“Sensei,_ ” Nagisa squeaked, at the same time as Ritsu. “On my side, my side!”

His position was shifted in a fraction of a second, tentacles whipping around him.

“ _WHERE ARE YOU INJURED, NAGISA-KUN?_ Sensei’s super-being slithery tentacle surgery will fix it at once!”

The mental image that conjured up, bizarrely, was of Kayano. He couldn’t really think about that further, though, because every inch of his being was objecting fiercely to Korosensei’s horrific volume. _“Korosensei,_ ” he hissed, agonising pain blurring his vision. _“please be quiet!”_

“…nyuya?” Korosensei inquired, voice now very small.

_“You’ve interrupted Nagisa-kun during an active cycle, Korosensei. He’s meant to be unconscious, this part is very painful!”_

Nagisa observed, through the blur of what was probably involuntary tears, the darkening colour of the teacher looming over him. “Sensei, stop.” He said, plainly. “I’m doing this voluntarily.”

Korosensei’s waving tentacles stilled. “Nagisa-kun?”

Nagisa blinked, to clear the water out. He felt it trickle down both cheeks. It itched. “The offer...came through Ritsu. I accepted.”

His teacher and assassination target was ominously quiet for several seconds. He heard Karasuma gasp for breath across the room. “…I see. And what exactly is this, Nagisa-kun?” A pause. “Can you explain why you can’t move?”

_“The headset is keeping him immobilised for his active cycle, sensei. It’s safer that way.”_

“This is an experimental procedure with optimistic chances of success.” Nagisa informed, closing his eyes. His voice felt thick, the words difficult to form. “If it works, it’ll be a real edge for assassination. Karasuma-sensei…he has nothing to do with it. I…needed, a safe place, to stay.” He panted a little, the urgency fading and the agony becoming far more insistent. “He offered. He’s only helping, Korosensei.”

The silence this time was much longer. Sensei blurred out of vision, and the next moment, a slightly cool cloth was being held to his forehead, only part of which was accessible below the headset. It soothed the headache a little – had his fever hit, then? “Nagisa-kun,” Korosensei said, and he opened his eyes. The super-being was all yellow again, the round face with its set-in-place grin so familiar it _ached._ “In the future, please remember: I am your teacher. I will help you in your attempts to improve. Even ones as poorly-advised as these.”

Nagisa smiled, gently. So _supportive,_ even in this… “Aa, sensei.” He murmured, closing his eyes again. “Next time, I’ll rely on you.”

“Good…but. I do hope there won’t be a ‘next time’, Nagisa-kun. My students shouldn’t harm themselves for the sake of assassination.” The cloth being held to his brow receded, carefully. “…Ritsu-san? If Nagisa-kun is meant to be asleep, please make him so. We will **_talk_** about this…”

_That sounds a bit scary,_ Nagisa thought, briefly. Then, very suddenly, he was unconscious.

**Notes for the Chapter:**

> This chapter, originally posted on tumblr, has undergone minor changes for posting here. Chapter 3 is live on tumblr.  
> Chapter 2 marks my first attempt to write Korosensei. There's a fair bit more of him next chapter, so any feedback on his characterisation would be appreciated there. He's easily the most 'anime' character I've ever written - it's virtually impossible to write him without the use of his weird noises. It's quite interesting.
> 
> I don't think the neurological problems this chapter or next are distressing enough to warrant warnings, but if people disagree, please let me know.
> 
> Many thanks to those who kudosed, bookmarked, and commented. It is all precious.


	3. Chapter 3

**Summary for the Chapter:**

> In which an ordeal is had.

Later, Ritsu told him that the third day was easily the worst.

In his lucid moments, he could recall parts of the last few days. He remembered sitting with Karasuma-sensei and trying to pull the disparate shards of memory together, trying to discern the mysteries steadily assembling in his brain. He remembered waking up on the hallway floor, with little idea of how he got there. He remembered waking up in excruciating pain, and talking one teacher down from killing the other.

He remembered almost nothing about the third day; not until the sun was dipping below the horizon, and the room had gone orange from the light through the curtains. He didn’t wake, so much as he became aware of being awake, sights and sounds transforming into something that had meaning, something that wasn’t just maddening noise. The room was red-and-orange and there were tentacles waving across his vision.

Nagisa stiffened at the sight of them, and they stilled.

“Nagisa-kun?”

 The voice was familiar, and easy to place. “Korosensei.” He identified, and tried to sit up. His muscles twitched, but did little more – held back by something. He looked down and found yellow twined around his limbs, far softer than the rope had been, but decidedly firmer. “…What time is it?”

 _“It’s 6.47pm, Nagisa.”_ Ritsu said, her voice unusually subdued. _“How are you feeling?”_

Nagisa took a moment to assess his physical state. He felt… _awful._ “Quite bad.” He admitted, noticing that his throat felt rough and sore, his voice unusually hoarse. His body felt like a giant bruise and the headache was wreaking havoc on his ability to form coherent thoughts. He looked up, and sure enough, Korosensei was there. The sight of him… “What are you doing here, Sensei?”

The super-being emitted a long, thoughtful noise. “Why, taking care of _you,_ Nagisa-kun!” He waved his tentacles cheerfully. Nagisa’s eyes tracked them unerringly, the sight making him feel oddly aggressive. “I have to say, I’m glad I found you last night~! Ritsu-san might have had trouble taking care of you on her own, I think.”

Nagisa noted that he was quite thoroughly restrained. A glance around revealed that he wasn’t in the futon at all – he was, in fact, suspended carefully in the air by a tangle of yellow appendages, his head and neck tenderly supported. “I don’t remember anything.” He ventured, uneasy. “Is it the third day? …the fourth?”

One tentacle retrieved a bottle of water, another carefully shook some vitamins out of their bottle. “Only the third, nuru-fu-fu~. You haven’t had a very good day though, I have to say.” The items drifted close to his face as he was manoeuvred, with painstaking care, into an upright position. The tentacles on his arms slipped away. “Can you take these, Nagisa-kun?”

Tentatively, he reached out. His fingers were shaky and weak as they closed around the bottle, and trembled too much for him to open it. Before he could even ask, a tentacle had solved that problem, whipping the lid off in a supersonic blur of movement. A supersonic blur that, interestingly enough, he had no problem following. “…Thank you, Sensei.” He tipped the bottle back and took several small gulps, finding that his throat rebelled at the motion, the gag reflex unusually sensitive. Nausea. He’d been ill today, then? He accepted the vitamins and took them one by one, spluttering a little as he fought not to gag. “I don’t suppose I’ve eaten much today.” Nagisa sighed, taking another sip of water before allowing the bottle to be taken from him.

“You _have_ had some difficulty keeping your food down, that’s true.” Korosensei agreed. “You’ve been quite ill – but still with a healthy bloodlust, I’m pleased to say.” He giggled, _nyu-hu-hu_ , as though tremendously pleased by this detail.

Nagisa observed his teacher warily. “Bloodlust, Sensei?”

 _“You have tried to kill Korosensei numerous times today.”_ Ritsu informed him helpfully from nearby.

“Quite unsuccessfully, as you can see.” The super-being’s head ran through with green stripes. “I have to wonder if this treatment of yours is worth it! You’ve made far better attempts in the past.”

Nagisa narrowed his eyes. “In the past, I wasn’t half-way through intensive brain modifications.” He retorted, blinking as he remembered…something brain-related. It suddenly occurred to him that this wasn’t the first time he’d had his brain thoroughly messed with, though details weren’t forthcoming.

“That’s true.” Sensei mused, wide grin as unmoving as ever. “Still, I think there’s been some improvements, hm? You have much better motion perception now~.” He flicked a tentacle past Nagisa’s face, insanely fast, but still well within his capability to track. He flinched, proving the point quite nicely. “We’ll see if you’re any better at killing me in three days…”

The words were vaguely ominous, in the way they tended to be when inviting kill-attempts. Confident and challenging, with a little mirth.

Nagisa stared at him consideringly, eyes flicking momentarily to the case in the corner. Quite abruptly, the vivid memory of packing it came to mind. He remembered other compartments, ones he’d never seen before. He _knew_ that computing lined the whole thing, nodes of memory and data storage in every corner, occupying even the carbon-nanotubules that were the primary reinforcement for the shell…it was _paltry_ , compared to what Ritsu had once had available to her, but the hardware in that case was ahead of anything available this far in the past.

“…Ritsu.” He murmured, thinking _hard._ “Are you alright? You have barely any sensors.” It occurred to him, for the first time, that she might be feeling as wrong as he was – disembodied, almost. Stuffed down into a weak and rigid form with far too little sensory input. The knowledge of _why_ he felt like that was _almost_ there, a memory at the root of everything…

Korosensei looked over at the phone inquisitively as Ritsu offered a vaguely uncomfortable smile. _“It’s fine, Nagisa. I’ve been branching out a little to compensate. We can talk about it later._ ” She looked significantly at their large yellow teacher.

“…Keeping secrets from Sensei, I see.” Korosensei said, morose.

Nagisa wasn’t paying much attention, though. He frowned, looking down, looking at limbs of yellow waving through the air and, feeling, like-

The tentacles stopped moving. The stillness was…soothing. Nagisa’s perceptions shifted with a disorientating jolt, and he realised he’d been on the edge of…something. Madness and grief and rage flickered at the edge of his thoughts, shaped like super-beings made of whipping shadows. He realised that he was sweating, breathing hard, out of nowhere-

“Nagisa-kun,” Korosensei said, keeping his many limbs motionless. “Ritsu-san and Karasuma-sensei refuse to tell me the purpose of this headset of yours, but I worry that it is giving you some unpleasant mental conditioning. You’ve been reacting quite unpleasantly to Sensei’s friendly tentacles today.”

He kept quiet for almost a minute, desperately trying to calm himself from the sudden…something. “Sorry.” He said softly. “I don’t know why, yet.” He felt…fragile. Like a paper lantern holding in a flame. His head hurt. Colours weren’t right, suddenly.

Slowly, a tentacle began to move, reaching for the water again. Nagisa’s eyes tracked it unerringly, the motion utterly arresting, utterly infuriating, _dangerous-_

 _“Sensei, Nagisa…”_ He heard Ritsu, her voice unusually worried. _“Nagisa, I think you might need to start your next cycle early. I don’t like the look of your brain right now.”_ Nagisa felt oddly cold at the words, but not afraid. Not worried.

“Ritsu-san, he hasn’t even had dinner yet.” Korosensei pointed out, his eyes slanting outwards in a hint of unease.

_“Try to take some more vitamins, it will have to do. Sensei, please fill up the headset with that fluid, too.”_

A little numbly, Nagisa accepted the water and several more vitamins, fighting against his nausea to swallow each one down, fighting against the mind that kept wanting to _remember-_

_“Quickly, Korosensei-“_

He felt a shudder run down his body, sickeningly strong, like he was undergoing a completely different procedure, like something was latching onto his mind, asking _what do you want to be/what can we make of you/what will you become_

_“Beginning cycle.”_

\---

The next time Nagisa woke up, he was alone with the Ritsu-phone, and he _understood_ what was wrong with his body and senses. He _knew._

“Ritsu,” he spoke, astounded at the realisation, “I was a super-being myself, wasn’t I?”

Red eyes blinked at him. _“You remember, Nagisa-kun?”_

“Not…really.” He admitted, raising an uncoordinated hand to rub at his eyes. “Not much. I…remember the tentacles asking me what I wanted to be.” He remembered sight and scent and sound and touch being so much _more_ than they were now, he remembered not being confined to two hands and feet and a rigid skeleton…

Ritsu’s face on the phone was more serious than she’d ever seen it. _“Do you remember what you said?”_

“I…” It was a _powerful_ memory, rooted through ­ _years_ of thoughts and emotions and experiences, like it was the foundation of everything that came after it.

_What do you want to be? What will you be? What will you become?_

Nagisa shuddered. “I remember.” And, with that in place, he could remember _so much more._ “Ritsu…I never realised how much it affected my mind. I spent decades, _decades_ , like that…” It was one thing to know, objectively, that you weren’t the same person you’d been before the treatments. It was another thing entirely to be in a normal body, feeling like _himself_ again.

 _“You were still Nagisa.”_ Ritsu asserted, sadly. _“You were different, but you were still Nagisa. You must remember me talking about it._ ”

He did. ( _“You’re different now, Nagisa. You don’t think or feel the same way about things anymore. You can’t tell, but it’s true.”)_ “I handed control over to you.” He recalled, rubbing at the side of the headset as if he could reach the skull beneath. He remembered long, _long_ years of complete _trust,_ moving at the behest of an artificial intelligence, trusting _her_ to know who he was when he couldn’t remember, trusting her to know what he needed to do… “Ritsu…” It was _overwhelming._

 _“…Nagisa._ ” Her voice was soft. He realised that he was crying.

“The others…they all died. Didn’t they.”

Her avatar peered at him, eyes hooded with sorrow. “ _It’s why you took the treatments. We couldn’t manage the job alone.”_

He nodded, jerkily, and breathed through the floods of emotion. The intensity was unfamiliar. He hadn’t realised how much the tentacles had dulled it. “It’s the fourth day?”

 _“It is._ ” Her avatar was less familiar to him by now than the electronic voice in his head, but it was still unbearably reassuring to see her there. _“Korosensei has decided to supervise you as much as he can for the rest of the process, but I sent him away for class so that we could speak.”_

“Korosensei…” Nagisa could remember the previous evening, a little. “He was here yesterday, wasn’t he? And something went wrong.”

 _“You were unstable the whole day, Nagisa, and quite ill too.”_ Ritsu put her virtual face in her virtual hands, as though tired by the memory. _“You had quite violent flashbacks throughout the day, and reacted badly almost every time Sensei moved his tentacles too quickly. You vomited every time you ate anything more filling than vitamins. I realised in the evening that, well, you were sort of at a tipping point – at a stage where you needed to have more done or your brain wouldn’t be functional. You...nearly had some very bad seizures.”_

He sort of remembered that. “Was that when you put me out early?”

 _“It was. It came on quite suddenly.”_ Ritsu’s avatar looked down, shame-faced. _“I’ll be watching more closely now. But you should be over the hill, so to speak – things should get easier.”_

“My memory is certainly better.” Nagisa agreed, looking dubiously at his trembling fingers. “These tremors, though…”

“ _They’ll get worse before they get better. It will be a while before you can work on them._ ”

“Well, after the last cycle.” He sighed. “So, have I given anything important away?”

 _“I’m quite sure that Sensei doesn’t know about the time travel yet._ ” His AI overlord claimed. _“He thinks you’re being conditioned to be aggressive towards him and is quite upset about it. He’s noticed the case, but taken me at my word that I’ll blow it up if he tries to get in or take it away. The rest of the class haven’t given anything away, either. Hopefully we can take him by surprise._ ”

Nagisa frowned, trying to recall. “With…the upgrade?” He muttered, brows furrowed. “That was one of the objectives, wasn’t it?”

 _“We only have the one vial for now. If you can get the drop on him, it’ll be enough. Otherwise we’ll have to make more.”_ She paused. “ _Do you remember any other objectives?”_

“…Kidnapping scientists?” He guessed, knowing it wasn’t right but unable to place the memory.

Ritsu giggled. _“Not quite, Nagisa. I suppose we’ll just have to wait for the next cycle.”_

\---

Nagisa was lucid enough that morning that he managed to get up, get to the kitchen, and fetch his own breakfast. Unfortunately, Korosensei ended up returning almost the very moment he began hacking that breakfast back up again.

“This is a bit embarrassing, sensei…” He muttered, not bothering to resist, as he was suspended in mid-air by tentacles and painstakingly cleansed. “None of it even hit me. You got a bucket at Mach-20 speeds and made sure I didn’t make a mess.”

“ _You are ill, Nagisa-kun!_ I will take _perfect_ care of you, or how could I face you as your teacher?!”

It was somewhat startling, to suddenly be in this position. Even without taking the time travel into account…Nagisa himself had never been on the receiving end of Korosensei’s pampering tendencies very much. There had been a couple of times that his teacher had fixed his hair up, but troublemakers like Karma had attracted the aggressive caretaking far more frequently. Then again, he’d never been visibly ill in the presence of Korosensei that he could remember, either.

He saw tentacles flash by, carrying- “Sensei!” He objected, turning red. “I can change my own clothes!” No matter how high-speed the change-over would be, he was perfectly happy _not_ to have his teacher implement a change of underwear, thank you very much. Thankfully, the tentacles stilled at his words, some of his own clothes from his teenage years hanging over them. “…Did you go to my _house,_ Korosensei?”

“Of course!” The looming yellow super-being proclaimed, cheerfully. The waving tentacles made a number of his old, old reflexes twitch unhappily, but they didn’t arrest his control like they had before. Thankfully. “No one else could do it, considering you’re meant to have been kidnapped, and you could hardly stay in the same clothes all week, Nagisa-kun! Ngyuuu~.”

Nagisa sighed, because actually, that was quite helpful. “Well…thank you, sensei. I can change on my own, though.”

“Hmmmm, well, if you insist,” Korosensei pondered, putting him gently down to the bathroom floor. “I’ll leave you for a while, then! I’ll be listening to make sure you don’t fall over.” In a rush of air, he was gone and the door was closed. His clean clothes were also folded neatly on the floor – and they were, in fact, pyjamas. Well…that seemed logical enough, since he was unlikely to be leaving the futon much.

Nagisa scrutinised the door for a moment, but decided against locking it. It wasn’t as though a locked door would stop Korosensei if he felt he needed to get in, after all. He went about his bathroom tasks quickly, fully aware that Sensei probably wouldn’t be held at bay for long, and sighed with satisfaction as he pulled on the provided (clean!) clothing. Pyjamas really were more comfortable than school clothes, too – they’d undoubtedly be far more suited for the task of laying around all day. He eyed himself critically in the mirror as he put the last button into place, fingers shaking hard enough that it took several tries.

His reflection was decidedly more haggard-looking than it had been before, with heavy bags under its eyes and an unhealthy pallor to its skin. The tremor looked much more alarming from a third-person perspective, too – honestly, he looked like he might fall over at any moment. He could sort of see why Korosensei was fussing so much.

Nagisa sighed at his reflection, untying his braided hair and making a token attempt to sort it all more neatly. He managed to get as far as picking up a comb, whereupon he apparently triggered Korosensei’s grooming senses or something, because the next second there was a mass of yellow brushing the door aside at astounding speed. The comb was snatched from his hand in mere moments, while other tentacles quested through the room in search of products.

“Let me take care of that for you, Nagisaa-kun!” Korosensei invited himself, promptly combing his hair out, applying dry shampoo, combing again, braiding, and tying in approximately the time it took him to say the words. Thus, in the space of several seconds, Nagisa found himself feeling significantly neater. The air around his head was also considerably warmer from the speed of Korosensei’s movements, but that was alright.

“...Thank you, sensei.” He offered, blinking. “Aren’t you supposed to be teaching at the moment?”

“Your classmates are doing some practice questions right now. I’ll go back to mark everything in a few minutes, hu-hu.” Sensei gathered Nagisa up into his tentacles without a further word, returning to the sitting room in a blur. “Your classmates are worried about you, you know. Ritsu-san isn’t telling them very much.”

 _“There are reasons for that.”_ Ritsu claimed, imperiously. _“Besides, there’s only two cycles left. They can wait._ ”

Her words were a balm to Nagisa’s soul. “Thank goodness.” He sighed. “Only two more…”

“How do you plan to return, Nagisa-kun?” Korosensei asked, setting him down on the futon and passing him an opened water bottle. “After all, your parents think you’ve gone missing. There will probably be a fuss, don’t you think?”

“Ah…well, I’m planning to claim amnesia, but I’m not sure about anything else.” He answered, frowning a little. “I’d prefer to avoid having to go to the hospital, not only because of the bills, but because of what they’ll find in the blood tests.” He made a face at the water, but had a little anyway. “If you’re in the picture now, sensei…do you think you could drop me in another city? That way I could just go to the police station and have them contact my mother…and I can refuse medical treatment more easily, too.”

His teacher nodded, wide grin bobbing up and down. “I would be happy to, Nagisa-kun. I’ll even supervise from a distance to make sure you get to the police station safely. Be sure to think about the details of your plan over the next few days. Make it an assignment, even.”

Despite everything, Nagisa couldn’t help but smile at that. “I will.”

“Good, good…” Korosensei’s tentacles waved out in approving ripples. “I have to return to your classmates now, Nagisa-kun, but I will come back soon!”

And, with that, he was gone, leftover winds ruffling the sheets. The cap of the water bottle settled into place by Nagisa’s phone. He sighed.

 _“Everything alright?”_ Ritsu inquired from the phone.

Nagisa waved a hand at his now-immaculate hair in answer. “Just…Korosensei.” He explained, putting the water down so that he could _lay down._ “He’s so…” He struggled to find the words to describe it.

 _“Himself?_ ” His oldest friend offered. _“Nostalgic? Familiar? Overwhelming?”_

“All of that.” Nagisa agreed, quite worn out by it all. “But especially the last. I’ve had so long to get over our graduation, but even so…”

 _“It’s different now that he’s actually here.”_ Ritsu sympathised. _“I understand. It was hard for me, too – except I process things more quickly, so I got over it not long after he arrived.”_

“Aa. Must be nice.”

“ _I suppose._ ” She harrumphed, simulated face falling into a pout. _“If I didn’t have all my work to do, I’d be so bored. Having so little processing power is_ painful _, Nagisa. I feel so…_ slow _._ ”

He held up a hand to watch it tremble. “I think I understand.” He said ruefully.

\---

Despite the fourth cycle having clearly helped, Nagisa wasn’t perfectly lucid the whole day. Later, when Korosensei returned, the sight of him was so profoundly shocking that he started choking on his own saliva.

“ _Koro….sensei?_ ” He gasped, in between coughs.

“Agh, Nagisa-kun, _breathe_!” The teacher in question implored, tentacles waving frantically, two of which went alarmingly close to his face. “Do you need me to do the Heimlich? Is there something obstructing your throat?!”

“I’m fine,” Nagisa wheezed, heart clenching in his chest as he looked up and _up_ at the tall super-being who had done so much for him. “Sensei…”

Yellow limbs rubbed soothingly at his back. “Hmm?”

“…Didn’t you die, sensei?”

The round, grinning face observed him for a moment. “Despite your best efforts, Nagisa-kun, I am very much alive.” He snickered, _nyu-hu-hu,_ and went momentarily green-striped.

Nagisa remembered the Shield of Earth flickering in the sky, and a knife in his hand, and so many tears he couldn’t see.

He decided not to argue. He was too tired to figure this out. “Okay, sensei.”

\---

By the evening, Nagisa could conclude that it was probably the best day of the procedure yet, despite his inability to eat much, and a few momentary lapses of awareness. This was largely due to the fact that he was lucid and coherent for _almost_ the entire time, and he even managed to fall asleep naturally when he got tired, rather than needing Ritsu to induce it.

Part of the credit, however, undoubtedly went to Korosensei.

As soon as he’d finished with classes, he shamelessly invaded Karasuma’s house to flagrantly pamper Nagisa. He bought all sorts of food from all over Japan, trying to find something that wouldn’t set off his nausea. He tested the articulation of his joints, and having deemed him stiff and sore from extended bed-rest, promptly transformed the bathroom into a makeshift spa for him.

Nagisa tried to insist that the manicure and pedicure were unnecessary, but he was thoroughly ignored. At the very least, there was no nail art, or even paint.

One of the most bizarre parts was probably the massage, given how unused to non-combative contact he’d grown, but frankly Nagisa had lived long enough that he could deal with the strangeness of it. He really _was_ stiff and sore, after all. Lying in one place for the majority of four days would do that.

Really, though, the strangest thing was being treated like a precious student again. He’d completely forgotten the thorough, thoughtful care that Korosensei had bestowed on their class – or, rather, he’d forgotten what it felt like. It wasn’t something any of them had ever experienced again after graduation, and the return to it was…soothing. Heartwarming, even.

Nagisa hardly knew what to do with himself. He supposed he’d never really gotten over Korosensei’s death. None of them had.

“Thank you for taking care of me, sensei.” He murmured, as he was presented with a warm cup of herbal tea. Surprisingly enough, it didn’t set off his nausea at all.

“You’re very welcome, Nagisa-kun.” A yellow tentacle extended to the other side of the room, returning with a book. “Now, I believe we have a few hours this evening…Ritsu-san tells me you should remember things you learn now, so why don’t we catch you up on your studies?”

Nagisa blinked, and glanced at Ritsu. She shrugged at him. _“You’re quite stable now, Nagisa. I think you should remember any new things you learn, at least a little.”_ She stared meaningfully at him. _“And it might be helpful to test things you already know, too.”_

He nodded, slowly, and obligingly turned to Korosensei. “Can we start with English?”

“Your best subject? Hm, I suppose you _are_ recovering.” The man tapped a yellow finger to his chin, contemplative. “Very well, then. I’d like you to translate these phrases for me…”

It swiftly became evident that he was, in fact, mostly fluent in English by this point. Evident enough that Korosensei swiftly noticed, posed him more and more difficult things to decode, and then eventually began flat-out conversing with him in the language.

“You were _not_ this good at English a few days ago, Nagisa-kun.” Korosensei observed, in the language being discussed. “Is this something to do with that headgear of yours?”

Nagisa answered slowly, and not just because he had to be careful about what he said. The words and knowledge were there, but his mouth wasn’t used to shaping the words, and it took longer to think about than he thought it should have. “The headset is artificially forming connections in my brain,” He said, enunciating every word with as much precision as he could manage. “I already know a lot of things I didn’t before. Soon, I’ll know more.”

Korosensei stared at him. As always, his grin didn’t change, but he did seem a little surprised. “Nuruu? That _is_ quite valuable. In that case, I understand your risk-taking better than before. Did you know how much you would be learning when you agreed to this?”

“I knew fluency in English would be included, and I was also given an estimate of the volume of the information.” Nagisa answered honestly. “What I’m ending up with is more than I expected, though.” His pre-procedure self certainly hadn’t guessed that he’d be receiving a head full of super-being reflexes, as well as over a century of memory.

“Very interesting, Nagisa-kun. Your English is certainly very good. Why, Nakamura-san doesn’t stand a chance at beating you for marks, now. She will certainly be annoyed!”

Nagisa laughed, remembering the tenacious woman that the tenacious girl had grown into. “Yes, I expect so.”

“And, the accent is interesting, too. I can’t quite place it.” Korosensei seemed earnestly intrigued, if his expression and tentacles were anything to go by.

His accent was a bit of a bastard amalgamation at this point, given the variety of people he’d been speaking with over the years. “Ah, it will be a mix of things.” He informed, thinking back on the English-speakers he’d communicated most with. British, Irish, Australian, American….he’d been exposed to almost every English accent under the sun. He paused, and added “I should be able to speak other languages, too.”

His teacher’s tentacles perked up, rippling with interest. “Oh, is that so?”

“None as well as English.” He nodded, a little bashful at the evident fascination. “But…hypothetically, I should know at least thirty languages now, at least to a basic conversational level.”

“…Nyuya?!”

\---

Korosensei ended up spending most of the evening testing his linguistic skills. He managed to run through Spanish, French, Russian, Mandarin, Korean, Italian, Thai, and Portuguese before he ran out of languages he was fluent enough to test. By the time Karasuma-sensei got home, Nagisa was helping Korosensei improve his skill in Catalan, a feat made quite easy by both its similarity to other languages and also Korosensei’s superhuman intellect. Teaching Korosensei was satisfying in the same way it was satisfying to teach AIs…or, well, superbeings. He just _learned_ things, soaking vocabulary up like a sponge.

Karasuma observed the clearly-not-Japanese conversation taking place on the floor in his sitting room with wary interest. “…I’m almost afraid to ask.” He commented, flatly, making his way through to settle in an armchair.

“Ah, Karasuma-sensei!” Korosensei greeted, cheerfully, waving a rippling arm in welcome. “Nagisa-kun is helping me with my language skills!”

Karasuma’s eyebrows went straight up. The _look_ he gave Nagisa made him flush like a schoolboy…which, technically, he now was. “…Nagisa, helping _you._ ” He voiced, neutrally.

“I know a lot of languages now.” Nagisa explained, a little embarrassed by all the attention.

“An understatement, Karasuma-sensei! I have to admit; the risk of permanent brain damage seems almost worth it for all this learning! And I’m sure there’s far more than languages involved if it was approved for my assassination, nyu-hu-hu…”

Nagisa smiled up at his teacher. It really was convenient how Korosensei easily accepted that the headset had to be for the benefit of killing him. Such egotism was _quite_ useful. “Honestly, sensei, I was a little worried you’d think it was cheating.”

“Information is an assassin’s greatest tool, Nagisa-kun.” Korosensei said, unintentionally echoing Karasuma. “And even if it weren’t, I’m your teacher…and a teacher is always happy to see his students learn.”

He’d had many of his own students over the years. He could agree with that. “On that note, Sensei…How about learning some more languages?”

The superbeing’s arm-tentacles flexed suspiciously. “Wouldn’t you prefer to learn something new yourself, Nagisa-kun?” Still, there was no disguising the hints in his expression and limbs; it was overwhelmingly obvious that he’d only require the slightest justification to agree. He smiled, reminded that his old teacher had himself never stopped learning while he was alive. And now, he _was_ alive. He could go on learning.

“It’ll help me integrate the new information properly, so I’d find it very useful.” Nagisa assured him. “Rehearsing what the headset has given me will help my brain adapt to it properly.”

As he’d expected, that was all that Korosensei needed to hear. The tips of tentacles wriggled with delight. “In that case, let’s try Arabic! Do you know that one?”

Nagisa laughed softly, a little self-conscious under Karasuma’s stare. “Ah, I do. I’d say it’s about as good as my Italian, though the writing’s harder. Would you like to start with that? Once you’ve memorised the essentials of the writing system, it will be much easier.”

“Perfect, Nagisa-kun! I’ll just grab some writing tools!”

\---

On the fifth day, the headset had imparted enough of the neurological changes that once-hazy memories were becoming concrete, and evasive information was now within his grasp. There was a significant downside to this: his future brain, which had adapted to far superior physical capabilities and a host more available limbs, was now wholly out-of-place in a regular human body. The shaking and tremors that had begun building were now severe enough that he couldn’t walk safely on his own, and he couldn’t hold even a water bottle without dropping it. Sometimes, a motion he’d intended to go in a particular way did the opposite instead, which generally led to his remaining limbs lurching suddenly in directions he’d not intended at all.

 _“I tried to mitigate the effects, Nagisa. I’m sorry.”_ Ritsu fretted, watching as he shook and trembled horribly at the mere action of sitting up. _“Even though I know so much about the brain, its systems are so inter-connected, I couldn’t leave out too much of some parts without making the whole thing fail…”_

“We prepared for this, Ritsu. I knew I’d be useless for a while after the procedure.” Nagisa reminded her, voice shaky and halting along with everything else. Frankly, he far preferred this state of affairs to the mental instability and delirium of the third day, but it was still a pain to deal with. On top of that, he was still undergoing dramatic neurological changes every day, and the headaches were _immense._ “At least my peripheral nervous system isn’t affected.” If they’d had to find a way to carry _that_ over, his heart might not even beat properly. Thankfully, it wasn’t a necessary part of the procedure.

 _“There is that.”_ She agreed, sighing. _“Still, once it’s finished we can get to work with your rehab. You should start plotting out the details for your return.”_

He smiled at her, lopsided and mischievous from his lopsided position. “Like you’ve not already calculated everything, down to the smallest detail?”

 _“If I do all of your prep work for you, you’ll never learn to do it yourself,”_ Ritsu sniffed, turning up her avatar’s nose. It was a well-worn exchange between the two of them. _“And then what sort of sorry assassin would you be?”_

“One who isn’t very self-sufficient, probably.” Nagisa agreed, sighing as he attempted to form a solid fist. He wasn’t very successful. “I’ll spend the day thinking through everything, I suppose. And then you can tweak my plan as you like.”

She giggled. _“Much obliged._ ”

Nagisa observed the empty bedside with a vague, lonely sense of loss. “I suppose since Korosensei won’t be here much today, we don’t need to watch our words, either.”

“… _Aa.”_ He and Ritsu exchanged a light frown. Korosensei, after all, was currently supervising the class at the pool he’d arranged.

While she’d arrived back within an acceptable time-frame, it wasn’t ideal. For one…’Shiro’ would shortly be making another appearance, while Nagisa was still incapacitated and unable to do much about it. Chances to strike at someone like that off of his home ground were few and far between. Ritsu could guess quite accurately how long it would be until the whole river debacle…but he couldn’t act.

 _“Soon._ ” Ritsu assured him, after a moment. _“I’m gathering resources. By the time you’re ready to use them, we should be set.”_

He nodded, once. Then he sighed, and started planning.

_So…how do I make sure not to end up spending weeks in the hospital when I reappear?_

\---

Karasuma returned earlier than Korosensei that day, considering his duties as a teacher weren’t exactly thick on the ground on a pool day. Quietly, he observed Nagisa’s inept attempts at almost any sort of voluntary movement, and efficiently set to work helping him.

“Thank you for taking care of me.” Nagisa murmured, as he was supported upright. Obediently, he opened his mouth to be fed the multivitamins, grateful that the nausea had mostly passed. He refused to feel any shame at his incapacitation as a bottle was held to his lips for him to drink.

“It’s fine.” Karasuma replied, and said nothing more on the matter. He was comfortingly direct: if he said it was fine, it absolutely was. Nagisa watched him, curiously, and…yes, he thought that all this hardship he was enduring might actually be increasing the agent’s respect for him. Always a good thing, that.

The evening passed uneventfully, for the most part, except for when Korosensei dropped in to find Karasuma feeding Nagisa, which he apparently considered his sworn duty.

“You weren’t here, and he needed dinner. There’s no sense in complaining.” Karasuma told the superbeing directly, sounding distinctly unimpressed with his hysterics.

 _“_ But thorough, tender care and maintenance is _my thing,_ Karasuma-sensei!” Korosensei near-shrieked, having plucked the bowl and spoon out of his colleague’s hands the moment he spotted them. Now, he loomed protectively between Nagisa and his other teacher, tentacles undulating with a sort of vengeful upset. “And besides, I’m clearly much better suited for it!” Several yellow limbs supported Nagisa in a perfectly comfortable upright position while one other guided the food to his mouth, an admittedly much more stable configuration than what Karasuma’s two hands had been capable of. Nagisa had to restrain a giggle around the spoon as he watched a guarding veil of tentacles form around him, the twitch to their movements practically shouting of petty outrage. “You’re always trying to find ways to be more popular with the students than me, Karasuma-sensei…”

“You’re delusional.” The accused instructor stated, flatly, taking his leave of the room with an irritated scowl.

“…You’re being quite rude to him, Korosensei.” Nagisa pointed out, in the wake of Karasuma’s exit, and watched the tentacular cradle ripple with sudden agitation. “Did you even apologise for strangling him the other day?”

Korosensei flailed a little, flustered. “Nyuaa….well…no. But that is…!” He scrambled for words, round face quivering with dismay.

If Nagisa were Karma, he’d likely have pressed it further, and made sly remarks about the example Korosensei was setting for his students, fanning the fluttering into full-blown paroxysms of penitence. He was not Karma, however, and didn’t have any particular drive to needle his long-lost teacher for petty amusement. “You should maybe do that soon, sensei.” He said, and diverted the topic in another direction. “In the meantime…”

His teacher’s movements settled a little, the small eyes in his round face peering at him inquisitively. “Hmmm?”

 The muscles in Nagisa’s face were as shaky as the rest, but he was still capable of controlling them: he affected a vaguely embarrassed, imploring smile, allowing the tremble to make him seem especially helpless. Physically, he was exactly that helpless against a being like Korosensei. Psychologically, though…

Weakly, with large soft eyes, he said “Sensei, I’m a little hungry still.” And waited.

An entire superbeing’s worth of tentacles exploded into impassioned, nurturing action. Distraction: success.

He did hope that Korosensei would apologise to Karasuma soon, though. Unwarranted strangulation seemed like something that could lead to grudges, if left to fester.

\---

Then, _finally,_ he was sitting by to be prepared for his final session. Korosensei efficiently refilled the headset’s nanomachine supply, fed him his pills, and gingerly lowered him to his futon. “I understand this is to be your last session with that headset, Nagisa-kun.” He said, ponderously.

Nagisa nodded, emitting a very relieved sigh at the idea. “I’ll need follow-up sessions for a while after, to make sure everything is settling correctly. But, unless something goes wrong, I shouldn’t need my spine tapped again.”

“Hmm…” The slow, dour curl of the tentacles indicated the turn of Korosensei’s thoughts. “…I would _very much_ like to know who offered you this...treatment.” The two broad digits concluding his main handling appendages gently lifted his braid out of his face, setting it over his shoulder.

Nagisa blinked at him, serenely. “Aa.” He acknowledged, and deliberately did not say any more.

The digits drew back. “Well then…goodnight, Nagisa-kun. We will talk more tomorrow.”

\---

On the sixth day, Nagisa woke with the knowledge that he was mercifully _done_ with having his brain rewritten, but also with the most uncooperative body he’d ever had to endure.

 _“Oh dear._ ” Ritsu looked very sympathetic from his phone’s screen as he demonstrated his inability to do pretty much anything beyond pointless flailing. _“That looks very annoying. Recovery might be longer than anticipated._ ”

Nagisa stared at her, and just about restrained himself from saying something very rude in the futuristic parlance that, given time travel, only they remained privy to. As it was, he likely wouldn’t have even managed to successfully shape the syllables.

“…Is this expected, Ritsu-san?” Korosensei asked, several seconds after Nagisa’s attempt to communicate mostly resulted in highly slurred spluttering. As to be expected at this point in the timeline, he was spurting mucus gratuitously, and had put down waterproof tarps to protect Karasuma’s house.

He couldn’t even communicate in _sign language,_ given the terrible coordination of his hands. He couldn’t even _scowl_ properly. And, of course, the headset had to stay on in the interests of augmenting his recovery for at least another day. It was technically active now, but since it was only reinforcing native functions rather than exercising its own, the pain was limited to frequent stabbing twinges rather than unrelenting agony.

 _“It isn’t_ un _expected._ ” Ritsu hedged. _“We knew that there would be severe disruptions in almost all systems involving voluntary movement, but it’s hard to predict exactly what will happen, given the complexity of the brain.”_ She paused. _“Thankfully, practice should cause rapid improvement, given the substances in his body. We should see significant improvement by the end of the day.”_ A pointed look was aimed in Nagisa’s direction, and he sighed, obediently setting to work flexing his fingers as a decent starting point. Of course, the movements were jerky and uncoordinated, but even that would help.

Korosensei observed him with concern for a while. “Nagisa-kun, is it safe for you to chew food at this point? Is there a risk of biting into your tongue?”

He blinked, surprised at the question. He’d not actually thought of that. Experimentally, he worked the muscles of his jaw, trying hard to keep his tongue still. The motion was difficult, but he thought he could keep his tongue clear well enough. Even so…he wasn’t certain. He shrugged apologetically as a response.

“Hm.” His teacher expressed, and then he blurred out of the room. A few seconds later, he returned with several cans of soup in a shopping bag, and a few limbs set out to the kitchen with them. “We’ll have to go with a liquid diet for now, to be safe!” He proclaimed, tentacles oscillating around him.

 _“That’s probably safest.”_ Ritsu agreed.

Nagisa tried to say ‘I really hope I can recover quickly’, but without the fine control of the many muscles involved in talking, it came out horrifically slurred, and probably well beyond the comprehension of even Ritsu’s voice recognition programs.

He sighed. And, because his speech wasn’t going to improve unless he practiced, he tried to comment ‘this is going to be a long day’.

_“…Maybe I’ll spend the day making a new speech recognition program.”_

\---

Nagisa didn’t start his attempts to recover in earnest until Korosensei left. As much as he knew that his teacher would never hold his repeated failures at coordination against him, he did still retain a measure of pride, and preferred not to demonstrate such a profound level of incapacitation in front of someone he admired.

Thus, once his teacher had left for class, Nagisa determinedly set to work with his rehabilitation. For the most part, this involved a lot of frenetic flailing in his futon while Ritsu observed his brain and prodded processes in the right direction.

The work of Ritsu through the headset was now far more involved. Where before she’d been growing his brain into the broad shape of what it had been in the future, now she was watching and applying her nanobots with pin-point precision. It required every ounce of the processing power they’d brought back in the case.

So, when he extended his arm and it didn’t work correctly, Ritsu was looking at the neurons firing in his heavily altered brain. With the nanomachines and their legion of synthesised proteins, she tried to reconcile the connections trying to form and the ones the headset had imposed, tying together all of the many, many loose ends. With luck, she might be able to preserve the good things – like his improved reaction time – while getting rid of the connections which relied on a very different body.

Essentially, she was overwriting a fair bit of the work she’d done over the last six active cycles. She had the extensive pre-treatment scan to go off of, so it wasn’t like she had nothing to refer to. However, to see where the problem areas were in the first place, he had to trigger them. Hence the flailing.

As one might expect, writhing energetically without pause was a fairly strenuous activity. Given his previous superhuman condition, Nagisa honestly wasn’t sure how to rate his current stamina – it had been a while since he assessed himself using human norms. At any rate, he ended up breathing hard with exertion after less than fifteen minutes of all-out activity, which was appalling by his remembered standards. He tested his ability to extend an arm and make a fist, and deemed it insufficient for the provision of the water bottle at the bedside.

By the time lunch rolled around and Korosensei dropped by to check on him, Nagisa was absolutely parched, and drenched in sweat. The futon was in a bit of a sorry state as well, but given his current level of coordination, it wasn’t really safe for him to exercise anywhere else.

He sighed with relief on seeing Korosensei, but kept his mouth shut, trusting Ritsu to communicate his needs.

“It seems you’ve not been neglecting your exercise, Nagisa-kun. I’m pleased to see it.” The supercreature observed cheerfully, several tentacles already in the kitchen going about their tasks.

 _“He’ll need food and drink, Sensei, and many of the vitamins.”_ Ritsu explained. _“A bit of a wash probably wouldn’t hurt, either.”_

Nagisa grimaced and nodded fervently, not at all comfortable with the way his pyjamas were sticking to his skin.

Korosensei gathered himself up, eyes gleaming. **_“It shall be done.”_ ** He intoned, tentacles expanding across the room in a garishly yellow lattice of movement. Nagisa eyed them, resigned, and waited for the cosseting to ensue.

\---

After a very speedy seeing-to of all of Nagisa’s requirements, Korosensei returned to class. He commented, just before leaving, that he might be back late, because ‘Terasaka-kun has recruited the class for an after-school assassination, nyu-hu-hu’. His head was distinctly stripy as he said it, quite clearly expressing his opinion on the likelihood of said attempt’s success.

The knowledge that his classmates’ lives would shortly be at risk, as well as his teacher’s, put Nagisa into a decidedly grimmer mood. About an hour after he was left alone with Ritsu, he began to worry that some small divergence might make things go badly wrong, and set to work focusing on the movement of his hands. Two hours after lunch, he’d recovered enough control of his fingers to sign, shakily, ‘ _Warn Korosensei’._ Korosensei’s name sign was, of course, a garbled blend of ‘kill’ and ‘teacher’.

Ritsu observed him with interest. _“About the assassination attempt this afternoon?”_

Slowly, Nagisa pressed his hands into service, forming _‘Yes’,_ and then _‘danger to team, danger to teacher’._

 _“So, warn him that there might be a danger to the class and to be on his guard?”_ She pressed.

 _‘Concerned about time changes’,_ Nagisa explained briefly, and continued _‘warn about scientist’._

The AI kept silent to prognosticate for a while, most likely considering the best options for the content of the warning. _“I will tell him that I have information on the movements of ‘Shiro’, and that he is orchestrating the event today through an unsuspecting Terasaka. I will tell him to be on guard regarding danger to the students and the threat posed to him by Shiro and Itona. Should I mention the allergen that has been used against him?”_

Nagisa took a moment to think. He raised his hands, signing _‘Yes’._

 _“Very well. I’ll dispatch the text message.”_ Her avatar stilled, very briefly. _“Done. I’ll let you know if he makes any reply. You should return to your exercises.”_

He sighed, some of his tension dissipating. With Korosensei forewarned, it was very unlikely that anything serious would go wrong. The man was more than intelligent enough to think of a thousand contingencies given their tip and the time available to him.

Clumsily, Nagisa saluted his AI overlord, and resumed his work.

\---

Their warning to Korosensei had yielded a quick response: a text reading _‘Thank you for the warning, Ritsu-san.’_ He didn’t ask about the origin of the information, but that was no guarantee that he wouldn’t later.

Nagisa spent his time flailing with a particular emphasis on his hands, since they were currently his best option for communicating. Ritsu noticed his focus and cut it short not an hour after the dispensation of their warning. _“Nagisa,”_ She explained, patiently. _“Garbled speech will alarm people far more than a bit of shakiness, and also most people don’t know sign language. Improving your speech is clearly your biggest priority at this point.”_

He sighed, conceding the point. He kept silent for several moments, consideringly, and then started babbling out the set of rules that had been affectionately nicknamed the ‘Tentaclauses’ by the recruits who’d had them drummed into their heads. Ritsu’s software had evidently progressed enough by that point for her to recognise it, because she giggled at him, evidently amused.

Once he was half-way through his second iteration of the regulations in question, Ritsu interrupted, saying _“Nagisa, there’s a much more fun way we could be doing this.”_

Her avatar looked suspiciously mischievous. He eyed her warily, and then jolted in alarm as his phone suddenly started blaring out quite familiar music. It only took a few bars for him to realise that the words had been omitted.

‘ _I’m not sure now is the time for karaoke’,_ he suggested to her, knowing that any complaint in this was likely very much a lost cause. Ritsu _adored_ strong-arming people into karaoke – it harked back to her early years as an AI deeply enamoured with music.

 _“Nagisa-kuuun,_ ” She crooned at him, the volume of the music abating slightly as she spoke. _“There has_ never been a better time for karaoke _. I’ll start you off!”_

Without further ado, she sprang into ‘singing’, which was really her just playing her voice singing the lyrics at a slightly lower volume than typical. Nagisa rolled his eyes at her, quite aware that there was no talking to Ritsu when karaoke was involved. It was really no surprise that their faction had ended up as the most musically-focused in space.

He opened his mouth, resigned to his fate, and started garbling the words of Senbonzakura in time with his AI overlord. She gave him two approving thumbs-up, and the volume soared.

Naturally, karaoke ended up being stupidly helpful for his recovery.

**Notes for the Chapter:**

> Notes: Korosensei is tricky, but I like writing the tentacles. Ritsu is a vocaloid at heart and adores music. ‘Senbonzakura’ is a vocaloid song by ‘Hatsune Miku’, who incidentally shares a voice actress with Ritsu. The song in question also has a Ritsu version in the Assassination Classroom soundtrack. I prefer it to the original.
> 
> Chapter 4 is live on tumblr. It's kind of long as a 'I took ages to write this' bonus, coming in at close to 11k rather than the usual 7 or 8.  
> I've made some changes to this chapter since it was posted on tumblr but for the life of me I can't remember what they are, so if anyone notices inconsistencies let me know.
> 
> As a final note, I'm currently somewhere with rubbish internet, so if I made any posting errors or the internet interfered I might not be able to fix it promptly.
> 
> Thanks to all who kudosed/bookmarked/commented. This is a quieter fandom than some but it's nice that I'm getting readers even so. Hope you all liked the chapter, and if you read 4, that one too.


	4. Chapter 4

**Summary for the Chapter:**

> In which assorted plans are ruined, changed, created, and executed.

**Notes for the Chapter:**

> Warnings: this chapter contains mentions of child trafficking and associated unpleasantness therein. There are more detailed warnings in the end notes if this worries you.

Ritsu alerted him to Korosensei’s approach around a second before he arrived, appearing perfectly well despite the potentially calamitous assassination attempt which had, presumably, been resolved. Sensibly enough, no one had taken their phones with them into the water, so Ritsu’s awareness of events extended only to the explosion of the river-dam, and a lot of panicked noise. They’d both grown quite anxious waiting for news.

“Good evening, Korosensei.” Nagisa greeted, words merely indistinct rather than incomprehensibly slurred. All of the singing had rather worn out his voice in the process, and it sounded a little rough as he spoke.

The yellow superbeing in question perked up, yellow limbs waving. The movement was worryingly subdued – he looked preoccupied. “Oho, I see you’ve made a lot of improvement in the last few hours, Nagisa-kun.” He observed, coming over by the side of the futon to inspect the various water bottles arrayed there. “Have you been able to drink on your own? It looks like the water level in this bottle is lower.”

Nagisa extended an arm, shakily, and made a weak fist. He couldn’t grasp with any particular strength, but he had reasonable precision now. “Opening the bottles is still quite difficult.” He admitted. “But I’ve managed. I’ve been focusing on my speech.”

_“We did karaoke. It really helped!”_ Ritsu, momentarily distracted from important things by her favourite subject, sounded absolutely delighted by her statement.

Korosensei made an intrigued noise at that, looking to Nagisa for confirmation. He nodded, adding “Hopefully, it wasn’t loud enough for the neighbours to object. But it did help.” Nagisa neglected to mention the many times he’d bitten his tongue and the side of his mouth as part of the recovery process. It was somewhat inevitable, after all. He shook his head, reminding himself of the topic at hand. “More importantly, Korosensei – is everyone alright? Is anyone hurt?”

The ever-active tentacles slowed to near-stillness. “…Everyone is fine, Nagisa-kun. Thanks to the warning from Ritsu-san, I was well-prepared for that Shiro-san’s tricks, and Itona-kun as well.” There was something odd in his tone at those words, something that made Nagisa frown. “…Actually, Nagisa-kun, it’s good you’re doing so well this evening. I’m afraid I may have to spend time elsewhere for a while.” It didn’t sound like a comfortable statement. The squirm of his tentacles was sort of heavy and close to the roots, which in body-language terms was an indicator of tension. The nervous flickering of the peripheral limb-tips, at the edge of Nagisa’s vision, hinted at agitation.

“…Sensei?” Nagisa asked, warily. “What’s wrong?”

The small eyes oriented on him, blinking. There was a pause. “I’m afraid Itona-kun performed much more poorly than his guardian hoped, given my preparations.”

_Divergence,_ he thought, with a sinking feeling. “He abandoned him?” He asked, sharply, leaning forwards. His arms were just about steady enough to support him in the endeavour.

Korosensei certainly looked surprised, now. “…Yes, he did.” He agreed, limbs shifting a little closer to his body, gathering in sinuous curves. “I’m afraid he isn’t doing very well. I must devote time to attempting to help him.”

_“Oh dear._ ” Ritsu said, undoubtedly beginning the process of revising many, many plans. _“Nagisa?”_ He glanced at her avatar on the phone. She raised her on-screen hands to gesture at him in concise military-sign, saying _‘changed circumstances. Thoughts on action?’_

Nagisa exhaled, staring at the screen. In the future, the use of the sign wouldn’t have been necessary, but it was very valuable here. Korosensei certainly wouldn’t know this breed of sign language. Carefully, he raised his hands to gesture back. _‘Potentially threatening. Last time solution complex, no guarantee repeat. Teammate endangered without help.’_ It had taken some tricky work to disconnect Itona from the tentacles enough to remove them, last time. They couldn’t guarantee the same things would happen this time, in which case the boy would die.

_“Agreed.”_ Ritsu murmured, aloud, and moved her screen-hands again. _‘Bring here and administer aid.’_ She flicked the gestures upwards at the beginning and end of the sentence; a command-imperative.

He nodded at her, and turned to Korosensei. “Bring him here, Sensei.” He said. Calm, but firm. “We can help him.”

Sensei’s many limbs drew _in_ , held close and ready near his body. His fingers settled atop one another in front of him. “…How so, Nagisa-kun?” His voice was quiet.

“His tentacles are a prototype.” Nagisa explained, flexing his fingers as rapidly as he could manage. He’d be needing manual dexterity soon. “Without maintenance, they’ll cause him extreme pain, and put such stress on his body that he’ll die within days. Most likely from heart failure, but he could also start having strokes. His body temperature will also steadily rise until he risks brain damage.”

“…You know about these implanted tentacles?” A ripple of agitation ran down a number of his limbs, and the words were in an unusually deep timbre. At this point in time, Korosensei didn’t know who ‘Shiro’ really was. He didn’t know how offshoots from his own tentacles had come to be implanted in humans. And, evidently, he was _very anxious_ to find out. Unfortunately, given the circumstances, he might end up finding out more than was convenient.

_“More headset knowledge, Sensei.”_ Ritsu said from the side, red eyes serious. _“Though, of course, I know everything Nagisa does. You’ll need his hands for this, though.”_

“We can help him.” Nagisa said, plainly. “Very quickly, as well. Bring him here, Korosensei.” It was unfortunate that they couldn’t ask Karasuma first, since he wasn’t home yet, but…well, a life _did_ depend on it. He probably wouldn’t mind.

The superbeing considered that for several seconds. His thoughts were quite easy to guess at: he wanted answers, but he wanted to ensure the safety of his student far more. Tentacles extended slightly, as though loosening. “Very well, Nagisa-kun. I will be back soon.” He blurred out of the room, disappearing from sight.

Nagisa sighed. “I think many of our initial plans just died.” He said, dragging himself with effort from the futon.

_“Violently so.”_ Ritsu agreed, blinking at him as he picked up the phone she was on. _“I’ve messaged Karasuma-sensei to know he’ll be hosting another teenager.”_

“Good idea.” Nagisa tested the function of his legs and found them sorely lacking. Grimly, he set about crawling towards the suitcase, on the other side of the room, primarily through use of his arms. He reached it, pressing a thumb to the outer interface to open up the keypad. “Code for the keepsake compartment?”

_“4-2-4-2-5-6-4-2-9-1-5-6-4-2-7.”_

He typed it in as quickly as he could manage with fingers that were still shakier than he’d prefer. The compartment opened with a click and a hiss; the second on the right of the suitcase. At first glance, it didn’t appear especially significant; the contents here were largely computing, as well as a few carefully-wrapped mementoes that Ritsu had strong-armed him into packing. He knew better, though – he brushed aside the false bottom underneath a few of Ritsu’s humming processors, peeling it back with care to reveal another security interface. He bent forward to present it his iris, and then all five fingers of his left hand in sequence. “Code?” He asked again, urgently.

“ _3-1-0-0-6-0-5-4-2-5-6-4-8-9-2.”_

By some miracle he avoided smashing the wrong keys, and the most well-fortified compartment of them all opened on mechanised doors. The section was small, but deep – and it contained the most potentially calamitous things they’d brought with them. There were no tentacle seeds, since those very much counted as organic, but there was pretty much everything but. Rows and rows of chemicals in labelled metallic phials blinked in the light, and he ran his fingers over them, picking out two tiny containers and two equally tiny syringe-and-needle sets. He withdrew with the items, and the compartment promptly closed with all the speed it had been designed for.

Korosensei returned with Itona just as he was closing the compartment, the case’s locks sliding together with tiny mechanical whirrs. Nagisa looked around urgently at the first hint of wind, cradling the precious items to his chest. They were very cold. “Is he conscious?” Nagisa asked, immediately, before the shape of his teacher and teammate had resolved fully.

Itona screamed, angrily, and that answered the question well enough. The sight of him was somewhat like a punch in the face. “Very much so, Nagisa-kun.” Korosensei said, loudly enough to be heard over the noise. “If you know how to help Itona-kun, please do!”

“Put him on the futon and hold him down.” Nagisa said, shaking off his initial reaction and beginning a furious crawl over to said location. He was expedited by a tentacle, arriving beside his patient with both medication and phone. He put everything down, carefully, and inspected Itona. His heart clenched – it had been so _long_ since he last saw him – but there were more important things to worry about than his emotions.

All of Itona’s awful prototype tentacles had been truncated to less than half a metre in length, though several were clearly in the process of regenerating. They were deep black and bloated with liquid, writhing in jerky and frenetic motions that alarmed Nagisa terribly.

_“Oh, that’s not good.”_ Ritsu observed, eyes wide.

“It isn’t.” Nagisa agreed, grimly, and supported himself on one arm while he bent over to check on Itona’s eyes. The blood vessels were all burst, the iris warped – and the _tentacles,_ his _temperature –_ he’d not seen rejection symptoms this bad in a _long_ time. What a _horrible_ prototype. “Itona-kun, can you understand me?”

“ _I’m strong!”_ The boy spat at him, wild-eyed, thrashing in his yellow restraints. “I’m stronger than you! I’m stronger than _all of you! I can kill you all!”_ He didn’t make any sort of comment as to why that mattered; evidently, he was in quite deep. He sighed, and settled into the bedside role from long experience.

“I’m sure you can.” Nagisa said, gently, reaching forwards to part Itona’s hair around one of the squirming tentacles. He felt at it, finding the skin around it swollen with unusually dark blood. Not nearly oxygenated enough. The tentacle itself, as expected, was very cold. “You’re very strong, Itona-kun. I believe it.”

“I’m stronger than _you_!” Itona snarled. “ _Get off_ me!” A little of the violence had ebbed at the verbal confirmation of his strength, though. Good.

“I’m here to make you stronger, Itona-kun.” He said, calmly, and sat back, watching his patient’s reactions as he reached for a phial. The tentacles produced a jerky, shuddering ripple – but the motion of it was almost approaching natural.

The boy blinked bloody eyes. “…Stronger.” He repeated, tonelessly. More aggression bled from his frame, and Korosensei’s tentacles shifted to better support him.

“I’m going to make you stronger.” Nagisa promised, slipping the needle onto the syringe. The tentacles shuddered again, and an unnatural pallor came over Itona’s face. He was, at least, struggling less. “You’ll be so strong. Stronger than everyone.” He murmured, soothing, and opened a phial. After a quick glance over to count tentacles, he pulled twelve millilitres of fluid out, and carefully wiped the needle on the edge of the phial as he withdrew it.

“I… _._ ” Itona mumbled, frowning. Abruptly, his tentacles exploded into violence again, held tightly down by Korosensei’s. His body, in contrast, seemed weaker, sagging into the futon. “I…I’m not strong enough now. The tentacles…they said they’d make me strong.”

“I know. I understand. You need to be stronger. I’ll help you.” Nagisa rattled off the words almost by rote, providing as much of a balm to the tentacle-gripped mindset as he could. “Lay here, and I’ll make you stronger. I’ll be injecting something into you that will make you stronger.” His fingers trembled a little on the syringe, but he was reasonably confident in his ability to wield it without wasting any doses. He reached forwards with the other hand to part the hair around the nearest tentacle again, murmuring repetitive platitudes as he went.

As expected, the first bite of the needle at the foot of a tentacle made Itona buckle again, screaming rage and pain. “It **_hurts._ ”** He snapped, eyes pulled wide. The ends of Korosensei’s tentacles wriggled anxiously at the assertion.

“Nagisa-kun?” The superbeing prodded, quite evidently fretting like a mother hen over this indication of suffering.

“Shh.” Nagisa said, more to Korosensei than to Itona. “It will make you stronger, Itona-kun.” Gently, he pulled the needle from the swollen skin. The tentacle there was already noticeably more sluggish than the rest, movements slowed and the dark bleaching out of it, second-by-second. “Sometimes pain is necessary to grow stronger. It was like that when you got your tentacles, wasn’t it?”

Itona blinked at him, caught between induced rage and memory. “…Aa.” He said, slow and confused. “It hurt a lot.”

“This will hurt, as well.” Nagisa told him. “It’ll feel like your skin is burning, in some places. You’ll have sharp pains in your head. Soon, your body will ache and you’ll be tired for a while.” He reached for a new tentacle.

His patient was quiet for several seconds, hissing as the second dose was injected. “It’s starting to burn around the first place.” Not a word about strength in that sentence – _good._

“That’s normal. I’ll give you a painkiller once I’m finished with your injections.”

“…It’ll make me stronger?” The voice was almost plaintive, now.

“It will. Please be patient for the procedure.”

Some of the blood was receding from his eyes. “…Okay.” He sighed, most of the remaining tension leaving him. The remaining un-dosed tentacles were still jerking frenetically, of course, but that was just how this ungainly prototype worked. Nagisa worked his way around them quickly, inspecting his dose each time to make sure he wasn’t giving too little.

Then, at last, he’d done it all. Nagisa injected the remaining drops into the tentacle closest to Itona’s temple, just to get rid of it faster. It was never good to have berserk tentacles too close to major blood-flow. “That’s your first injections done, Itona-kun.” He said, sitting back. “How are you feeling?”

“The pain is getting worse.” The boy admitted, brows furrowing. He looked up, and his eyes were almost entirely back to normal. It struck Nagisa, suddenly, how _young_ he was. It felt almost like a physical blow. “And my tentacles feel…numb.”

“That’s also normal.” Nagisa inspected him, deciding that it was probably too soon to reveal that the tentacles would shortly be falling off. He reached to the side for his pill bottle, removing one of the painkillers. He glanced at the Ritsu-phone for input, hand hovering over the multivitamins, and she nodded, so he extracted two of those as well. He presented them to Itona with an unopened bottle of water. “Please take these. There’s a painkiller, and some vitamins to help your body deal with the procedure. Drink as much of the water as you can. It’s important to stay hydrated.”

Itona, so _young_ , was evidently quite used to medical procedures from Yanagisawa’s dubious care, because he didn’t hesitate at all. He took the bottle, opening it with an easy twist that Nagisa wasn’t quite capable of yet, and he downed all of the pills with practiced ease. He stopped after drinking maybe a hundred millilitres, and Nagisa fixed him with a _look_ until he muttered ‘tch’ and drank some more.

“Very good, Itona-kun.” Nagisa praised, earning a confused blink from his charge. Something seemed to occur to him.

“…Aren’t you one of Nii-san’s students?” In the periphery, Sensei’s tentacles squirmed with discomfort at the address.

Nagisa eyed Itona’s own tentacles. They were all drooping, near-motionless, and almost completely white now. “Call him Korosensei, Itona-kun. He isn’t actually your brother. Tentacles don’t mean brotherhood.” He corrected, firmly. “But yes, I am.”

The pale-haired boy’s gaze was owlish. “Shiro didn’t mention anything about you being involved.” He said.

“He doesn’t know everything.” Nagisa informed him, and looked up at Korosensei.

His teacher had been conveniently compliant for the whole time, submitting to what appeared to be superior expertise on Nagisa’s part. It was a little difficult to read his mood at the moment, since his facial expression was quite unhelpful and his tentacles were occupied, with their ends only indicating the discomfort that he could have guessed anyway.

Undoubtedly, there would be many prods for information later. Nagisa sighed, and returned to his patient. He put down one syringe and reached for the next, filling it up with a more sizeable dose. “This is your last injection for now, Itona-kun. It will help mitigate the damage that the tentacles have done to your body.” He reached for an arm, pausing. “Ah, Korosensei? Could you get the first aid kit?”

“Of course!” A tentacle shot off, and returned in seconds. “What do you need?”

“Alcohol wipes, please.” The requested item was removed from its packaging and passed over. Nagisa accepted it with his free hand, and then wiped at the crook of Itona’s elbow. “I’ll be injecting now.” He warned, and then stabbed neatly into the vein. The boy twitched, but didn’t otherwise react.

“…The tentacles damage my body?” He asked, after a moment.

Nagisa wiped at the injection site with the disinfectant as he removed the needle. “They did. You see, Shiro-san implanted you with an unstable prototype tentacle. They do offer great strength, but at considerable cost. Most of the maintenance you’ve needed is simply because it’s an unstable experimental version.” He offered the wipe to Korosensei, murmuring “Cotton and tape, please.”

Korosensei, guessing his goal, simply reached forwards with several filament-thin white tentacles, reducing the tiny puncture on Itona’s arm to nothing.

“…That also works.” Nagisa said, ducking his head briefly. “Thank you.”

“Is there anything else I can help with, Nagisa-kun?” The superbeing inquired.

He considered it, bending forwards to inspect the base of one tentacle. The swelling was already decreasing noticeably, and would likely dissipate completely once the anti-inflammatory in the injected compound kicked in. “No, it should be fine.” He said, sitting back. “Itona-kun? Are you feeling aggressive still?”

The boy blinked yellow eyes at him. “…No, I guess.”

“It should be fine to let him go, Korosensei.” The restraining tentacles held for a moment, then released, gently settling Itona on the futon as they withdrew. Nagisa watched their motion keenly,  then returned to his poor young classmate. “Can you stand?”

Silver brows furrowed, ever so slightly. “Of course I can.” He stated, and then proved it, rising to his feet. The tentacles fell limp around his shoulders as he did so.

“Take one of the seats, then. I’m going to discuss your recovery and future with you.” Nagisa told him, gesturing to Karasuma’s armchairs. He took hold of the two partially depleted phials and slipped them into his pocket, taking hold of his phone and two bottles of water before he started shuffling awkwardly towards his own chair.

Itona, who had navigated to the seat with ease, stared at him. “Why are you crawling?”

Nagisa batted away Korosensei’s tentacles, saying “I need to do this myself, sensei, but thank you.” One-armed, he pulled himself up into the armchair that was almost opposite Itona’s, and sat back with a sigh. “I’m very weak at the moment, because I’ve been undergoing my own procedure. I should recover in a few days. Incidentally, that’s what this headset is for.” Itona straightened at the word ‘weak’ – the tentacles’ influence was still there, clearly. Nagisa reached over to pass a bottle of water, before carefully taking his own. Opening it was a hardship, with his weak grip. “Now, Itona. I’m going to discuss your medical matters quite plainly. Are you comfortable having Korosensei here?”

Yellow tentacles rippled indignantly at the thought of being expelled, but Nagisa was more concerned with Itona’s comfort. He might have guessed that it wasn’t a concern, though. “I don’t care.” The boy said, predictably, accepting the water bottle awkwardly into his lap.

“Alright then.” Nagisa inclined his head. “Korosensei, you may as well take a seat as well.”

“I think I will.” The tall superbeing didn’t fit well in an armchair, and settled onto the two-seat sofa instead. “May I ask questions?”

How refreshingly direct. “It depends on the question, but yes. I have to speak to Itona-kun first, though.” He replied, calmly, and straightened to face the boy in question. “Now, then. I mentioned the damage done to your body. Your prototype tentacles have very negative effects on both your body and your mind. Without proper maintenance, these effects become fatally severe very quickly, especially when you are fighting with the tentacles for long periods. This is why your condition worsened so quickly today.”

“…Shiro usually gave me medications after a fight.” Itona said, face characteristically impassive. “Is that why?”

“Aa. They were necessary to reduce the impact on your system.” Nagisa nodded. “With extended use, even with the right maintenance, your tentacles would have eventually killed you. They have all sorts of terrible effects – they raise your blood pressure, increase the likelihood of blood clots, drastically increase your stress levels…you might have lasted a year or two, with careful maintenance, but you were likely to die either from a heart attack or from something related to blood clots – like a stroke, for example, or a pulmonary embolism. Without maintenance, that would happen in anything from hours to days after a fight.”

A pale hand went up to feel at one of the hanging tentacles. Undoubtedly, there was no feeling left in it at all. “…You did something to them, didn’t you?” His fist clenched around the tentacle, but there was little anger on his face. Mostly resignation.

“I did.” Nagisa agreed. “The first agent I injected will be dissolving their connections to your nerves. Once that’s completed, they will simply fall off. The remaining damage should heal on its own.”

Itona released the tentacle. His hand fell back into his lap. “And the second?”

“Anti-inflammatory, to reduce the swelling caused by your tentacles. Also an anticoagulant, to thin your blood and prevent clots. You should avoid bleeding or getting bruised for the next few days.”

The boy stared down at his hands. “You said you were going to make me stronger.” He didn’t tend to have a great deal of inflection in his voice, but it was there now; just a hint of upset.

“I will.” Nagisa said, and the boy looked up, pale eyes wide. “To start with, Itona-kun, you can’t be strong if you’re dead, so I’ve already helped you there. For the rest, though…in our assassination classroom, we learn many kinds of strength. I know you’re not fond of schoolwork, but that gives you one kind of strength. We learn others, as well. We have daily lessons in fighting, and we have teachers who are happy to give extra instruction. Korosensei here will also be happy to help you become stronger in the ways you personally find important.” The teacher in question nodded eagerly, a pleased ripple passing over his peripheral limbs.

Itona had made a face at the mention of schoolwork, but looked somewhat thoughtful at the rest. “You want me to be a member of the class. Really, not just as a show.”

“Aa.”

He digested that for several seconds, then leaned forwards. His expression was intent. “You said _you_ were going to make me stronger.” He said, leadingly.

Nagisa eyed him warily. “Yes…?”

“You know a lot about the tentacles,” Itona said, and oh, Nagisa knew where this was going- “You know about versions better than what Shiro gave me. Can you give me the better ones?” There was a fair bit of heat in the words.

Nagisa looked at him. He glanced at Korosensei, who would have appeared merely politely interested if not for the twitching at his tentacle-tips. Then he sighed, and looked back. “I could, Itona-kun,” He said frankly, watching the shocked undulation of yellow on the sofa. “But I won’t.”

The tentacles couldn’t actively grip his thought processes any more, but the habits of thought remained. Itona scowled, fingers clenching into fists. “ _Why?_ ” He demanded.

“My apologies, Itona-kun, but you’re a very bad candidate for tentacles.” He informed, demurely. “If Shiro-san had known more, he would never have chosen you. A drive to be stronger, or a strong drive for _anything,_ is almost always a bad thing for a tentacle user.”

Itona’s eyes would have been red again, if the tentacles had still been live. “Then why was I so _strong,_ if I was such a poor candidate?!” He was tense again, as though poised to spring from the chair and attack.

Nagisa sat calmly in place. He had a large yellow bodyguard, after all. “That was the inherent strength of parasitic tentacles. It had nothing to do with you. If _you_ want to be strong, look elsewhere; tentacles can’t help you.”

“Shiro said-!”

“Shiro-san lied.” He cut in. Itona froze mid-sentence, face scrunching up. “Shiro-san wanted a test subject, and you merely seemed convenient for him, as you had no one supervising you who might object.”

“…Nagisa-kun.” Korosensei said, perhaps in protest. It was a fairly blunt and ruthless way to say it, after all.

Itona held still for several seconds, then sagged like a puppet with cut strings. “Fuck.” He muttered, fists still held tight in his lap. He breathed deeply, almost viciously. Nagisa sat quietly while the boy processed everything, waiting until he looked a little calmer to speak again.

“You don’t need tentacles, Itona-kun.” He claimed, and the boy looked up. He looked so _young_ , he could hardly stand it. “Once I’ve recovered, I’ll personally work with you to help you improve. And, if you like, I’ve got some technical projects you can help with.”

A spark of interest broke through that near-desolate expression. “…Projects?” He asked, near toneless again.

“Computing and assorted electronics, for the most part. All will be far more advanced than what’s available on the market.” Nagisa watched the spark ignite, and pushed a little further. “That should be good, if you want to take over your parents’ factory, right?”

Itona stared at him. There was a hint of suspicion there, but… “Yeah.” He said, and paused. “…When will you be recovered?” The fact that he asked was, for him, a sign of considerable interest. Nagisa smiled.

“I hope to be back at class within a few days, but that depends. You should join the class and get used to things, and I can start you on the projects when I return.”

The boy frowned, thinking. Several silent moments passed, and then he nodded. “Alright.”

Nagisa sighed, admittedly relieved. “Good. Well then, I’ll let you know what to expect from your health over the next few days…”

\---

He spent a while longer explaining to Itona that he’d be prone to tiredness for a while, and also was highly likely to experience phantom pain in the tentacles even once they’d fallen off, which should happen by morning. He might experience headaches while he recovered, and would also probably have mood swings for a while. To be safe, Nagisa claimed that he’d need to be put into the neural reprogramming headset to check everything over after a week or so.

Karasuma got back while Nagisa was warning Itona not to mention his tentacle expertise to the class, and Nagisa turned to greet him.

“Ah, Karasuma-sensei.” He said. “Sorry for the imposition. Is it alright if Itona-kun stays here tonight?”

Karasuma entered the living room and inspected the boy in question. The two of them exchanged similar impassive stares. “It’s fine.” He answered, stepping closer. “I heard you were in poor condition, Itona-kun.”

“…This guy helped.” Itona said after a moment. “I’m fine.”

“I see.” The agent looked over at Korosensei, whose tentacles had been quite still for a while now. “Will you be making their dinner, or should I get started?”

Korosensei sprang from the sofa at the mere implication of having the duty stolen from him. “I’ll cook dinner immediately!” He shrieked, limbs abruptly active again, and blurred into the kitchen. The three of them watched him go.

“He’s loud.” Itona observed clinically.

“He certainly is.” Nagisa agreed, ruefully. He offered his phone, Ritsu having remained silent for the whole talk. “Anyway, Itona-kun. You know Ritsu, right?”

He glanced down at the screen, dubious. “What’s the Autonomously Thinking Fixed Artillery doing on your phone?”

_“My name is Ritsu now, Itona-kun.”_ Ritsu told him, brightly. _“I’ve had significant changes to my code since we last met, and I also have data on a number of topics. I’ll be directing your and Nagisa’s projects.”_

Itona blinked. “You have schematics?” He guessed.

_“And the knowledge of the science and processes required.”_ Ritsu agreed. _“If you like, I can provide you with some reading material for while you wait.”_

“I’d rather learn on the job.”

_“That’s alright, then.”_ Ritsu nodded amicably, and then oriented her avatar to the side. _“Nagisa, you should put the chemicals back in the case now.”_

“Oh, right.” Nagisa tutted at himself, and worked himself carefully out of the armchair, crawling back towards the suitcase. “Sorry.”

Karasuma walked over to observe as Nagisa went through the involved process of getting to the chemical compartment, Ritsu rattling off numbers from a few metres away. His eyebrows raised at the decoy compartment. “Is that a _book?_ ”

“It’s two books.” Nagisa admitted, with a sigh. He peeled back the false panel again. “Keepsakes. It’s a waste of space, but Ritsu insisted.”

_“I get to keep my most precious things in my databanks. You should have the same privilege.”_ Ritsu called in response.

Nagisa leaned forwards for the eye-scanner as Itona inquired, flatly, “What’s with the suitcase?”

“I’ll explain it to the whole class when I return.” He answered, withdrawing the phials from his pocket as the compartment opened. He put them back into their places with careful, metallic clinks. Ritsu promptly closed it before Karasuma could look too closely. “It’s important that everyone finds out at the same time. That’s why I’d like you to avoid mentioning that I know a lot about implanted tentacles – that knowledge is related to my procedure and this suitcase.”

Itona grunted, and Nagisa took it as agreement.

\---

Later, when everyone had eaten and Korosensei had been conspicuously hovering near Nagisa for a while, he conceded to the inevitable.

“Korosensei.” He said, politely. “Was there something you wanted to say?”

Tentacles quivered. “Quite a lot, Nagisa-kun.”

Nagisa nodded, smiling serenely. “If you could take me to the gym, I’ll do some exercises while we talk.” Karasuma shot him a sharp look, and Nagisa gestured soothingly. “If that’s alright?”

“That’s perfectly fine.” Sensei decreed, gathering him up in a tangle of yellow. After a comparably gentle acceleration, Nagisa was in Karasuma’s small downstairs gym, which was equipped with a treadmill and a weight bench. The latter was quite worthless to him for the moment, but he could just about walk now, so the treadmill would be useful. He shuffled carefully onto it, and started it up at a very slow pace.

“I suppose you have a lot of questions, sensei.” Nagisa observed, setting Ritsu into the slot ordinarily used for water bottles. She looked out at him with interest.

_‘Plan change?’_ She inquired, with quick and brusque gestures.

_‘Improvisation’_ He returned, and waited for Korosensei’s response.

“I certainly do, Nagisa-kun. In fact, I’m not sure what I should be asking first.”

Nagisa stared straight ahead, walking slowly, and considered what he was going to say. “I’m going to withhold the most significant information for now, sensei.” He said, eventually. “I can tell you that the headset taught me everything you’re curious about. I won’t tell you who sent me the headset, or how they knew the things they programmed it for.”

There was an abrupt, annoyed flick at the tips of several limbs. “Then what _will_ you tell me?”

He thought. “I’m happy to provide information on the function of implanted tentacles.” He offered. “And I’ll answer questions if they won’t give away the information I’m protecting.”

Sensei produced a grumbling sigh. “Very well, Nagisa-kun.” He paused. “The agent you injected near Itona-kun’s tentacles. What is it?”

“A poison that selectively targets tentacle cells.” He answered, smiling ruefully. “So, yes, it will work as a poison on you. I expect it would only kill you if it were injected close to your heart, though.”

The tentacles offered an intrigued ripple. “Interesting. Will you be sharing it with your classmates?”

“Unlikely. It’s not a very efficient way to kill you, after all. It wouldn’t work well if ingested, and it would be difficult to inject enough of it precisely enough to finish you off.” He explained. “It inhibits regeneration, so it could potentially be useful there, but considering how difficult it is to make, it isn’t worthwhile.”

“Hmmm~” Korosensei put a yellow finger to his face in mock-thoughtfulness. “So, in other words, it’s mainly useful for removing implanted tentacles safely.”

“Exactly.”

“Fu-fu…very interesting. Any more interesting poisons in that case of yours, hm?”

Nagisa beamed at him. “Now, that would be telling.”

His teacher’s eyes slanted as he laughed. “Nuru-fu-fu-fu. Very well, I’ll wait to be surprised.”

“Anything else, sensei?”

The animated motion of his many limbs slowed a bit. “…You mentioned a technical project to Itona-kun.”

“I did.” Nagisa nodded, reminded. “Actually, I’ll be wanting your help with that, sensei. You see, we’re planning to tunnel into the mountain to create a secure underground bunker. I’m sure I could convince the class to help, but you’d be able to do the tunnelling most quickly and discreetly.” He reached out to pause the treadmill, and took his phone.

Korosensei’s tentacles waved in a sort of slow, baffled curl. “…An underground bunker.”

“The contents of the suitcase aren’t safe enough. They also require some assembly, which needs to be done in a secure and secret area.” Nagisa nodded. “Also, Ritsu needs to increase her processing capabilities to be able to function properly, and we need a safe place to store her servers. There’s a lot of reasons for the bunker. Will you help?”

“If it’s to help my students, of course.” The superbeing answered, slowly.

_“Excellent.”_ Ritsu proclaimed, and shifted the screen. Nagisa stood in front of Korosensei and displayed it to him.

“This is a diagram of the entry-way.” Nagisa explained, pinching the image to zoom in on the relevant area. “We selected this area, part-way up the cliff, as the primary entrance. It can probably be hidden quite well there. We want to put a short corridor in, with a decoy living quarters. If you can, Korosensei, I’d like you to develop that area into something you would plausibly live in. That way, if anyone finds it, they might think it’s one of your hideouts.”

A small drop of sweat ran down Korosensei’s head. “One of my hideouts?” He repeated, nervously.

“Yes, like the ones you make in the shape of your head. But more subtle.” Nagisa agreed, Ritsu giggling out of the speakers. Korosensei, predictably, started on some flustered twitching at that. “Also, you might want to keep this one tidy, as an example to the students who will be seeing it.”

The teacher was, by now, earnestly sweating. “A-ah, Nagisa-kun…”

“And please, no pornography shrine.” He requested politely. “Okajima-kun might be badly distracted.”

“Nyuya?!” Korosensei’s tentacles drew back in shocked, frantic arcs. “S-sensei has no idea what you’re talking about!”

“I’m sure.” Nagisa said, agreeably. “But, at any rate, this entry area can be customised to your taste, as long as it’s all kept hidden. Concealed in the area will be the opening for a modest elevator shaft.” He moved the image, showing the descent. “The actual elevator will take a while to construct, so we’ll have to use a makeshift ladder in the meantime.”

“…Are you being provided with funding for this?” Korosensei inquired, tentacles calming slightly at the indication that his hideouts weren’t going to be further discussed.

“No, not at all.” He admitted, sighing. “We’ve been given all the aid we’re going to get, and the construction project should stay a secret from the many governments with their eye on you. If it’s not a problem, I’d like your help with moving materials, sensei.”

“As long as it doesn’t interfere with class.” He allowed.

“Thank you.” Nagisa zoomed out of the basic schematic and switched to the 3D modelling software that Ritsu had compiled for his phone in about five minutes. “So, this is the main part.”

Korosensei stared. “Nagisa-kun.” He said. “That’s not a bunker, it’s an underground complex.”

“It will contain a bunker, though.” He pointed to a section of the blueprint helpfully labelled BUNKER, accompanied by notes on its various functions.

“…So I see.” The superbeing observed.

“We mainly just need the big space dug to those specifications, for now.” He hesitated. “If you could start as soon as possible, it would be wonderful. Itona-kun should be fine without extra help now, and so should I.”

“And I suppose you will want this done discreetly?” Two yellow appendages curled at the edge of his vision in a thoughtful sine.

“It’s very important that the site remains secure. And secret.” He nodded.

“From who?”

“Everyone except the members of the class and the teachers.”

The face of an early-type superbeing was generally not given to nuance: it was impossible to see any flicker of sharp interest in Korosensei’s tiny eyes. The tentacles said more than enough, though – for those who knew how to look, they were very expressive indeed. “This does make me _very_ curious about your mysterious benefactor, Nagisa-kun, if this is to be secret for almost everyone.”

He smiled guilelessly. “My ‘benefactor’ will know about the bunker.” He said, in perfect truth. “It wouldn’t make sense otherwise.”

“Why not leave the case with your benefactor, if you trust them with its contents?” The teacher inquired, handling appendages crossing at his front. One yellow digit tapped the other in a sort of thoughtful motion.

Nagisa hummed, glancing over at Ritsu. She shook her head, minutely. “I won’t be answering any more questions about my benefactor.” He said, calm, and tapped the treadmill’s display to incrementally increase his walking speed.

“You appear to take direction from Ritsu-san.” Korosensei observed.

“She’s much smarter than me, and more knowledgeable.” He shrugged, and said nothing more.

_“You flatter me, Nagisa!”_ Ritsu chirped from the nearby phone, before peering in Sensei’s direction. _“But I think you should stop answering questions now.”_

He saluted, smiling ruefully at Korosensei. “Ritsu has spoken.” He shrugged again. “If you have some questions later, I’ll see if I can answer.”

The tentacles slowed in their perpetual motion, just a little. _Unpleasant thoughts,_ the movement said. Of course, his voice gave none of that away. “Nagisa-kun, one more question, if you will.” _I am worried,_ expressed the increasingly drawn-in yellow motion. “These changes that have been made to you…is there any conditioning involved? Are you obliged to obey certain people or orders, or have certain reactions to things?”

Nagisa blinked, and looked at Ritsu for permission. She did not seem especially concerned by the line of questioning, and waved at him dismissively. _“It’s fine.”_ She told him.

He paused the motion of the treadmill to face Korosensei properly. “There’s no imperative for me to follow certain commands, or the orders of anyone in particular.” He said. “My free will is intact. I have the capacity for making my own decisions. However, I now trust Ritsu far more than I did before, and if I’m uncertain of something, I’ll trust her judgement above my own.” He hesitated, then added “Also, I am very vigilant regarding tentacles.”

Korosensei had looked as though he wanted to comment on the information about Ritsu, but the last part seemed to interrupt that intent. “’Vigilant’, Nagisa-kun?” He asked, almost sharply. The irregular wriggling at the end of his handling tentacles quite handily communicated his discomfort.

“I am very aware of tentacles moving in my vicinity.” Nagisa confirmed, unbothered by the superbeing’s reaction. “If any move very quickly towards me, it will register like a weapon moving towards me – like a fist or knife, for example.” He didn’t have the reflexes or speed to accompany that instinctive vigilance, now, but…it was still useful. He smiled disarmingly. “Don’t worry, Korosensei. I’ve not been programmed with any particular aggression – it’s just a higher level of awareness.”

Some of the unease left the motion of his teacher’s appendages, but there was still a certain disquietude there. “Hmmmm….” Korosensei expressed dubiously, and then he pelted a tentacle at Nagisa’s face, creating a slight _whoosh_ of displaced air as it went. Naturally, it stopped before making any contact, and he blinked at the yellow now within his focal range. “You didn’t show any reaction then, Nagisa-kun.”

“That’s because it wasn’t very unexpected, Korosensei.” He explained. “I’d flinch or react if you made sudden movements when I’m off-guard or not expecting it, but you were quite obvious just now.”

“Nyu?” The round yellow head tilted slightly, colour hinting at the incipience of green. “I suppose you are much better at following my movements now, nyu-hu-hu…”

Nagisa smiled, and said nothing.

“Well then. I look forward to seeing what effect this has on your assassination, once you’ve recovered.” The green that had been threatening to appear spread with force across his skin. “Of course, you will have to improve a great deal to have a chance, Nagisa-kun! _I do hope this was worth it,_ nuru-fu-fu…” He chuckled ominously, looming slightly as his eyes put off light.

“I hope I will not disappoint you, Sensei.” Nagisa answered placidly, utterly unbothered by the teacher’s showiness.

“As long as you try your best, you will never disappoint me.” The superbeing declared, tentacles adding emphasis with a surge of movement. “Well then! If you are doing well now, I will get to work on your secret underground lair!” His handling tentacles performed a dramatic flourish, less an expression of mood and more a display of personality, and then he sped away with a soft _boom_ and a localised gust of wind.

_“He’s quite bothered by all of this.”_ Ritsu observed, drawing his attention back to the screen.

“Aa.” He agreed, restarting the treadmill at a slow walk. “He doesn’t know where these tentacles are coming from, after all, and now you and I have shown up with such significant alterations, too…”

_“It must be very disconcerting.”_ She nodded. _“It’s good he’s agreed to dig the tunnels, though. Construction would take far longer otherwise, with much more of a security risk.”_

“We did think it was likely he’d agree. It’s not very difficult for him, and he’s gone to greater lengths for students before.” Nagisa shrugged, pausing the treadmill again to shake out his legs and try to gauge their level of mobility. “It’s true that you need space for processing power, for example, so it’s a very good reason for him to go to the effort.”

_“Oh, I can’t wait to have some proper hardware again.”_ Ritsu bemoaned, shifting track rapidly to wistfulness. _“I’m not used to being this slow, Nagisa. I don’t like it.”_

“You were much slower, once.” He told her, amused. “Imagine if we’d not brought all of the computing with us. What would you have done then?”

_“Failed miserably at everything, obviously, because I wouldn’t have the processing power to run my up-to-date self.”_ She harrumphed.

He snorted softly. “Well, wait a week or so, and we’ll have you closer to living in the style to which you have become accustomed.”

_“A week.”_ She sighed forlornly. A week was, after all, a very long time in AI terms.

“You’ll survive.” Nagisa put the treadmill on to a considerably faster setting, then regretted it as one of his legs stuttered mid-motion and tripped him up. “Ow.” He muttered, having fallen on his front. The treadmill had, at least, shut off – he had sensibly attached the clip-on safety cord.

_“Still shaky.”_ Ritsu commented critically.

“Yes, but that’s not a bad thing. I need to look somewhat incapacitated when I return.” He countered, getting back onto the treadmill. “In fact, I hesitate to practice much beyond getting a good grasp of walking back. Once I can walk fairly reliably at four kilometres per hour, maybe…”

_“You should be ready to go back tomorrow, then. Have you decided on the plan yet?”_

“I think I should be dropped at a city not too close to Tokyo, but not too far either, otherwise they won’t want to send me back without hospitalising me first.” He answered, restarting his slow walk. “As it is, I expect I will have to spend some time in police custody.” A pause, and he continued. “I’m thinking I should show signs of long-term restraint, and perhaps drugging. Some more chloroform, perhaps. Then it would be less odd for me to lack memory for such a specific time-frame.”

_“If you were supposedly unconscious for most of it, certainly.”_ Ritsu acknowledged, her avatar’s brow furrowing in a splendid simulation of thoughtfulness. _“Nagisa, have you considered implicating some real people in your capture?”_

He blinked. “As in, frame someone?”

_“It could be a good option. Korosensei should agree to plant evidence, and then you won’t have to worry about faking amnesia.”_

“I’d only consider it if I could frame someone who is genuinely a criminal of that scope already.” He dipped his chin a little lower, pondering it. “Do you know of any child trafficking rings operating in Japan that we could use?”

_“Not at present.”_ She said. _“But give me some time to do some in-depth hacking, and I ought to have some candidates for you.”_ It was, after all, a sad fact of present society that there were plenty of places for such people to exist, and therefore plenty such people _did_ exist.

“Thank you, Ritsu. Let me know if you find anything?”

_“Of course.”_

He stared at the treadmill for a few seconds, then sighed. “Well, I’d best stop this until we know what we’re doing.” If he did end up going with the brain damage story, he wouldn’t want to be too coordinated, after all.

\---

A little less than two hours later, and Ritsu had hacked her way through enough computers, chat rooms, and phone records to have a very decent idea of several unsavoury operations they could implicate. They convened in the sitting room to discuss and plan, Itona off to the side on one sofa and Karasuma observing sharply from an armchair.

_“If this one in Tokyo itself checks out, it would be quite convenient.”_ Ritsu said, voice emanating from the phone’s speakers even as he looked over information on its screen. _“Otherwise, rings such as these do tend to move their ‘acquisitions’ quickly, so it would make sense for you to be found in another city.”_

“There are child abduction rings operating in Tokyo?” Karasuma asked, disgust curling in his voice. His frown was quite fierce.

“It’s the capital city, sensei.” Nagisa answered, softly. “Of course there are.” He redirected his focus to Ritsu. “Whichever one we decide on, please send in some anonymous tips on the others, once we’re done.” He requested, frowning at the thought of all the appalling crime and injustice that existed in today’s world. It had taken an apocalypse and the eradication of most of the human race to manage it, but…at least their future, whatever else its problems were, had been rid of most crime for a long time. It was unpleasant to think of how much suffering was going on at that very moment.

_“Once I’ve invaded enough of the Internet, I’ll be doing more than that.”_ Ritsu agreed, quite darkly. _“In any case, I’ve sent a message to Korosensei asking him to stop by tomorrow. He ought to be happy to do some scouting for us, especially given what we’re asking.”_

Korosensei, while he had been a fairly indiscriminate assassin for his whole life, was not wholly without morals. He disliked, very ardently, the exploitation of those who could not defend themselves. “Ask him for an estimated time of arrival.” Nagisa suggested. “We’ll want to send him a message shortly before to warn him of my physical state. He might…overreact, otherwise.”

_“Sensible.”_ The AI nodded.

“What’s wrong with your physical state?” Itona asked, apparently finally curious enough to break through his semi-drug-induced apathy.

“Well.” Nagisa switched on the front-facing camera on his phone to inspect his face. “I’m in fairly good condition at the moment. It would add realism if I changed that.” He was quite pale and tired-looking, which was a convenient side effect of a near week of dramatic brain alteration, sickness, and drugging. It was a good start. He inspected his wrists, thoughtfully, then looked back at his face in the phone. “What do you think, Ritsu? Bruises on the face?”

Ignoring the slightly puzzled look from Itona and the displeasure from Karasuma, Ritsu hummed. _“Maybe some light grazing, and a worried lip?”_ She suggested. _“As if you got hit into the ground.”_

Nagisa nodded, eyes casting around the sitting room floor. “Most of the floors here are too delicate for it. The downstairs escape tunnel, maybe.” It had very basic concrete flooring, and ought to do the trick. “What else? I was thinking rope burns.” He indicated his wrists.

_“That would work well.”_ Ritsu nodded. _“Perhaps make it look like you’ve been restrained at different times, with some marks partially healed?”_

“That will be easier if I can get Korosensei to partially heal some marks.” Nagisa looked at his slim wrists. He knew that he bruised and marked up quite easily as a human, so that would work in his favour. “Same for miscellaneous bruising.”

“Nagisa-kun.” Karasuma cut in, voice and expression very severe. “I am not comfortable with you injuring yourself for the purpose of appearances.”

“That’s very kind of you, sensei.” Nagisa smiled slightly, and dipped his head. “However, I am very comfortable with it, and a show like this will greatly improve my cover. I won’t deal myself any damage that will leave a lasting mark, so it’s not a problem.”

“You’re pretending that you were kidnapped by criminals to cover your procedure,” Itona voiced slowly, yellow eyes largely unconcerned by the subject matter. “And so to make it seem more real, you’re going to get real injuries?”

“That’s right, Itona-kun.” Nagisa smiled at him, more brightly. “When playing a role to fool others, it’s important to use props to make it seem realistic. An infiltrator may use accents, mannerisms, certain items, or even physical changes to improve their cover, and therefore chances of being believed.”

“Is it necessary in this case?” Karasuma demanded. “You will have been missing for a week, with witnesses to show that you were taken by force. Who would question your claims?”

“Thoroughness is always important, Karasuma-sensei.” Nagisa said, firmly. “In this case, if they suspect that I’ve been dosed with certain substances, or hit, or restrained, they will be less likely to look for more problematic things – like the nanomachines in my bloodstream, for example.” He paused. “On the other hand, we don’t want to give the impression of something severely traumatic, so the damage can’t be too…suggestive, so to speak. Marks of extended restraint, perhaps the sort of bruise you acquire when trying to escape…”

“How will you be claiming to have escaped in the first place?” The man asked after a moment, still scowling, but seemingly a little closer to accepting his reasoning. “And what will you do if the men arrested deny having ever seen you?”

Nagisa sighed. “Easiest would be for me to be actually captured, but that’s too risky. I’ll ask Korosensei to plant blood and hair for me, and if necessary leave a paper trail to accompany the electronic one Ritsu will be adding. With that evidence, no one will believe the criminals if they claim not to have seen me. As for my escape – that depends on which location we end up using. I’ll be able to engineer a realistic story then.” He shrugged. “Until then…where’s that rope you were using to restrain me before, sensei?”

Karasuma stared at him for several moments, very considerably displeased, then swept his scowl to the side. “I left it in the hallway cupboard.”

He nodded gratefully, and stood up to go and fetch it. “Thank you, sensei.”

\---

It took some insisting, but eventually Nagisa was allowed to damage himself in peace. He did require assistance for some of it, though.

“Tie my wrists behind my back, please.” He asked Karasuma at one point, staring insistently until he was finally obliged, and then he made several corrections on the tightness and placement before becoming satisfied. He then spent the next hour pulling against the ropes until his wrists were raw and bruised, the skin broken in some places. He had the rope relocated to lower on his wrists and then repeated the process.

After that, he had himself gagged, then went downstairs to the secret escape tunnel and hit his face into the floor a couple of times, carefully simulating the sort of scrapes he might get if trying to escape restraints in a very awkward position. In the end he succeeded in getting some nice, realistic scrapes, and also pulled at the gag enough to get some light damage around his mouth.

Unfortunately, he couldn’t convince Karasuma to hit him or grab him to get some good realism bruises, and while Itona seemed unconcerned about beating him up for show Karasuma wouldn’t allow that either. Nagisa went to bed slightly disgruntled with that failure, and in the morning set about trying to argue Karasuma into compliance.

“It’s not an issue, sensei.” He said insistently, in a departure from the serene and demure affect he tended to prefer. “You won’t cause any permanent damage, and it will be useful for the cover. I’m quite literally asking for it and besides I’m sure you’ve given me worse bruises in training before. I don’t see what the problem is.”

Karasuma was, by this point, looking slightly more receptive to the idea. However, since he had very little facial expression on the best of days, that wasn’t saying much. “One problem, if nothing else, is that I have no wish to be strangled again.” He said, dryly.

Nagisa stopped, considering Korosensei. “Ah.” He looked at his phone. “When is he coming, again?”

_“Not long now.”_ Ritsu assured, and so they sat and waited for Korosensei to arrive.

As expected, the superbeing fretted extensively over Nagisa’s self-inflicted injuries, even though he’d been pre-emptively warned. Also as expected, he jumped at the chance to heal one set of wrist abrasions to make it seem older.

“That’s enough, Sensei.” Nagisa said, not long after the filaments began their work. “Any more and it will be implausibly healed.” His teacher pretended to ignore him, so he got firmer. _“Sensei._ If you heal it too much, I’ll just have to do it again. Stop now.”

“A teacher is not meant to allow his students to come to harm, Nagisa-kun.” Korosensei muttered darkly, his fine tentacle filaments withdrawing with palpable reluctance.

“Don’t pretend you’ve not done worse for the sake of a cover,” Nagisa said, and received a sharp look from Korosensei, Ritsu, and Karasuma for his troubles. He realised that he wasn’t meant to know about Korosensei’s extensive background in assassination, and promptly abandoned the subject. “And besides, I need to have more marks than this. I’ve been trying to convince Karasuma-sensei to help me with realistic struggle bruises.”

Yellow went wild with agitation. _“Absolutely not!”_ Korosensei near-screeched.

Nagisa blinked at him. “Well, Sensei, if your investigation shows that the children in these locations are in very good condition, perhaps that won’t be necessary.” He said, diplomatically. “In the meantime, could you heal the damage and swelling from my spinal taps? I’d like to avoid that being visible on scans.”

“…Of course, Nagisa-kun.” The superbeing muttered, and redirected his healing filaments. It unsurprisingly felt much better to move his neck once that was done, and then he stood up, visibly unhappy. “I suppose I had best go do some scouting now.”

“It would be appreciated.” Nagisa inclined his head politely. “If you’re not comfortable with it, I can return to the amnesia story. However, this plan is more believable, and furthermore will have some criminals apprehended and children rescued, hopefully.”

“I can’t fault your reasoning, unfortunately.” Korosensei said, sourly, and gathered himself. “I’ll be back soon.” With that, he was off.

\---

When Korosensei returned, having successfully completed a stealth reconnaissance of several sites, he was black-skinned and trembling with rage. The report made for very heavy, very unpleasant listening. Once he was done explaining the details of the various locations, Nagisa reached out and put a hand on one of his tentacles.

“Thank you for helping, Sensei.” He said, softly. “Remember, we’ll have those children safe soon.”

“I’m not certain ‘soon’ is soon enough, Nagisa-kun.” There was a low, angry timbre to the teacher’s voice, and his tentacles were roiling with anger. The one Nagisa had touched had stilled, though. “If it wouldn’t compromise your cover, I would rescue _every one of them_ , _**tonight**_ **.** ” Steam exhaled from his mouth as he spoke the last word.

“Crime won’t be solved in a single night, Korosensei.” He reminded, not unsympathetically. “It’s on Ritsu’s agenda to help tip off the authorities about operations like these. In the meantime, might I suggest arranging poisonings or accidents for some of their captors? Something to disrupt their procedures enough to prevent bad things from happening until the arrests.”

It…didn’t exactly sit well with him, either. He had at his disposal a superbeing who would gladly remove every one of those children from danger within the hour, but because he needed a good cover story, he was delaying. It didn’t soothe him much to think that, without their intervention, these children would never be rescued at all. He was still allowing injustice to continue, if only for a short while.

He sighed, and deliberately moved on. “Considering the information you’ve brought, the one based here in Tokyo seems best.” As it happened, the organisation was loosely connected with certain individuals in the local Yakuza family, though what evidence there was quite clearly indicated efforts towards plausible deniability for both sides. It seemed likely that the traffickers would not receive Yakuza protection from the law if they ‘screwed up’, so it was a decent target.

There was also the fact that children taken by this ring were generally sold onto buyers or other traffickers…’untouched’, so to speak. Though there was certainly rough handling, it didn’t seem to go further than that in most cases. They also didn’t give the children any addictive drugs.

Nagisa considered the information he’d been given, and deemed the detail insufficient. “So, to begin with, what was the state of dress of most of the children?” He asked, settling in for a long interrogation. He had a lot of details to consider, after all.

It took a long time to exhaust everything he or Ritsu could think of, and Itona, who’d elected to stay for the talk, was looking quite uncomfortable. Korosensei himself was persistently black-skinned, steaming with rage, and occasionally slipped into a reverberating snarl of a voice that was really quite threatening. Karasuma didn’t seem much better, and was scowling more fiercely than Nagisa had ever seen before.

Nagisa pursed his lips, and turned to Karasuma. “I think you’d best help me with those bruises, sensei.” He said, firmly. The man _glared_ , and Korosensei hissed like an angry snake, but in the end Karasuma nodded and Korosensei didn’t object. He stood and jerked his head in the direction of the escape stairs, both because it was away from Korosensei and because a simulated struggle likely wouldn’t be good for the furniture.

Unfortunately, Korosensei elected to follow. Itona was either not curious enough or too uncomfortable to do the same, so he stayed where he was.

_“Korosensei, you may wish to avoid supervising this.”_ Ritsu advised from Nagisa’s phone as they headed downstairs. The superbeing merely shook his head and continued following, so, well. That was his choice.

Nagisa stopped in the concrete escape tunnel and considered what to do. “I think grab my forearms from behind, Karasuma-sensei.” He said, and turned to offer the arms in question. There was a foreboding silence before he heard the shift behind him, and then hands clamped down on his arms. Nagisa nodded, and then set to struggling with all his might.

In the end it was a slightly traumatised duo of teachers that took him back upstairs, and Nagisa was feeling quite guilty for putting them through it all. He had gained some nice hand-shaped bruises on his wrists though, as well as some knee bruises from being shoved on the ground, and a good hand-bruise on one shoulder. They caused a variable amount of pain; a couple of them had been selectively healed, and were less raw.

The rest of the day passed with miscellaneous preparation: between classes, Korosensei chose the most plausible location for him to ‘break’ from – a ground-floor room with a particularly decrepit and rusty pipe running up one wall, and a window only just big enough for someone Nagisa’s size to squeeze through. The glass was already cracked from some prior incident, and wouldn’t be implausibly difficult to shatter. Shortly before Nagisa’s official escape time, the pipe would appear to have been pulled from the wall by the occupant tied to it, and the window broken using the sole stool in the room. On the window’s glass shards, Nagisa’s blood would be placed, as well as some choice fabric and hair strands. Nagisa spent the prep time being mildly drugged, because it seemed that the children there were sedated with chloroform or rohypnol when unruly and it wouldn’t do to have no traces of it in his bloodstream.

The clothes Nagisa had been kidnapped in, incidentally also the ones he’d been sweating in for several days, were wiped over the room to collect some authentic grime and maybe even hairs and such, and it was into these that Nagisa changed when the preparations were nearly ready to go. He rubbed some more grime into his hair, got himself nice and unkempt, and then declared himself ready at close to midnight.

What this meant was that Korosensei took him (minus phone) to a nearby rooftop while he prepared the apparent escape room, leaving the rope and blood and hair and such inside the room while Nagisa removed a piece of a broken glass bottle he’d filched from Karasuma’s recycling when no one was looking. He successfully sliced his clothes and himself up with believable broken-window-crawling damage before Korosensei could return to protest, then waited.

“ _Nagisa-kun,_ ” Korosensei hissed, _very_ unhappy, when he came to see the blood seeping through pieces of ripped clothes. “That was _not_ necessary.”

“Given the apparent escape route, I think it was.” Nagisa disagreed, handing over the bloodied glass. “Could you dispose of this somewhere non-incriminating, please?”

A little unsettlingly, Korosensei ate it, glass crunching between his teeth as his skin blackened further. Then he followed the plan, and set Nagisa a short distance from the house, where surely the occupants would be coming to investigate the ruckus soon. “I’ll be watching, Nagisa-kun.” He said, quiet and serious. “Good luck.” Then he vanished into the shadows of the night; not visible, but close by.

Nagisa took a deep breath, feeling the aches of the bruises and the sting of the cuts. Then, still dazed from the drugs and unsteady from the neural rewiring, he staggered with feigned desperation along the pre-planned route to either a helpful bystander or the police station – whichever came first.

Nagisa stumbled through darkened streets, watched over by his teacher, and settled breath by breath into the role he was to play.

**Notes for the Chapter:**

> Detailed chapter warnings: Some medical stuff, involving needles. Later, there is non-detailed discussion of child trafficking and illegal activities related to this, including drugging of children and abuse of children. Nagisa also causes himself physical harm to improve his cover, and convinces Karasuma to simulate a struggle to add some realistic bruises in.
> 
> Chapter notes: Next chapter will involve Nagisa returning to the world and dealing the consequences of the cover he chose. Additionally, chapter 5 has been posted on tumblr, and I will shortly be posting a new Assassination Classroom fanfiction called New Growth.
> 
> Content notes: references are made in this chapter to events which only appear in the manga. Namely, the contents of one of Korosensei’s hideouts, which he uses as a sort of getaway where he can be a shameful slob without worrying about being a bad influence on 3-E.


End file.
